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Technical Vocational Stream

Learning Resource Material

Computer Hardware and Architecture

(Grade 11)

Secondary Level

Computer Engineering

Government of Nepal

Ministry of Education, Science and Technology

Curriculum Development Centre

Sanothimi, Bhaktapur

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Publisher: Government of Nepal

Ministry of Education, Science and Technology

Curriculum Development Centre

Sanothimi, Bhaktapur

Layout by Khados Sunuwar

retrieval system or transmitted, in any other form or by any means for commercial

purpose without the prior permission in writing of Curriculum Development

Centre.

Preface

The curriculum and curricular materials have been developed and revised on a regular

basis with the aim of making education objective-oriented, practical, relevant and job

oriented. It is necessary to instill the feelings of nationalism, national integrity and

democratic spirit in students and equip them with morality, discipline and self-reliance,

creativity and thoughtfulness. It is essential to develop in them the linguistic and

mathematical skills, knowledge of science, information and communication

technology, environment, health and population and life skills. It is also necessary to

bring in them the feeling of preserving and promoting arts and aesthetics, humanistic

norms, values and ideals. It has become the need of the present time to make them

aware of respect for ethnicity, gender, disabilities, languages, religions, cultures,

regional diversity, human rights and social values so as to make them capable of

playing the role of responsible citizens with applied technical and vocational

knowledge and skills. This Learning Resource Material for Computer Engineering has

been developed in line with the Secondary Level Computer Engineering Curriculum

with an aim to facilitate the students in their study and learning on the subject by

incorporating the recommendations and feedback obtained from various schools,

workshops and seminars, interaction programs attended by teachers, students and

parents.

In bringing out the learning resource material in this form, the contribution of the

Director General of CDC Dr. Lekhnath Poudel, Pro, Dr. Subarna Shakya, Bibha

Sthapit, Kumar Prasun, Anil Barma, Romakanta Pandey, Dr. Sanjiv Pandey, Dinesh

Khatri, Ramesh Rimal, Jonson Khadka is highly acknowledged. The book is written

by Satyaram Suwal and the subject matter of the book was edited by Badrinath

Timalsina and Khilanath Dhamala. CDC extends sincere thanks to all those who have

contributed in developing this book.

This book is a supplimentary learning resource material for students and teachrs. In

addition they have to make use of other relevnt materials to ensure all the learning

outcomes set in the curriculum. The teachers, students and all other stakeholders are

expected to make constructive comments and suggestions to make it a more useful

learning resource material.

2076 BS Ministry of Education, Science and Technology

Curriculum Development Centre

Table of Contents

UNIT - 1 ....................................................................................................................... 1

Introduction to Computer ............................................................................................. 1

UNIT 2 ....................................................................................................................... 40

Computer Memory ..................................................................................................... 40

UNIT - 3 ..................................................................................................................... 53

Processor .................................................................................................................... 53

Unit 4 ......................................................................................................................... 90

Storage Devices.......................................................................................................... 90

UNIT - 5 ..................................................................................................................... 95

Input/Output Organization ......................................................................................... 95

UNIT - 6 ................................................................................................................... 105

Mobile Computing ................................................................................................... 105

UNIT - 7 ................................................................................................................... 118

Computer Assembly ................................................................................................. 118

UNIT 8 ..................................................................................................................... 138

Troubleshoot and Repair Maintenance .................................................................... 138

Computer Hardware and Architecture 1

UNIT - 1

Introduction to Computer

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

Content Elaboration:

1. Introduction to Computer

1.1 Basic Introduction to Computer

A computer is an electronic machine that takes input from the user, processes the given

input and generates output in the form of useful information. A computer accepts input

in different forms such as data, programs and user reply Data refer to the raw details

that need to be processed to generate some useful information. Programs refer to the

set of instruction that can be executed by the computer in sequential or non-sequential

manner.

In other word computer can be defined as an electronic device that stores, retrieves,

and processes data, and can be programmed with instructions. A computer is composed

of hardware and software and can exist in a variety of sizes and configurations.

Hardware

The term hardware refers to the physical components of your computer such as the

system unit, mouse, keyboard, monitor etc.

Software:

The software is a set of instructions that makes the computer work. Software is held

either on your computer hard disk, CD-ROM, DVD or on a diskette (floppy disk) and

is loaded (i.e. copied) from the disk into the computers RAM (Random Access

Memory), as and when required.

CHARACTERISTICS OF COMPUTERS

The characteristics of computers that have made them so powerful and universally

2 Computer Hardware and Architecture

useful are speed, accuracy, diligence, versatility and storage capacity.

Speed

Computers work at an incredible speed. A powerful computer is capable of performing

about 3-4 million simple instructions per second. It works in the fraction of second.

Most of the computers work on Micro and Nano second. Its speed is measured in term

of MHZ(Mega Hertz) and GMZ( Giga Hertz).

1 millisecond= 10-3 Seconds = 1/1000 s

1 microsecond= 10-6 Seconds = 1/1000000s

1 nanosecond = 10-9 Seconds = 1/1000000000s

1 picosecond = 10-12 Seconds = 1/1000000000000s

Accuracy

In addition to being fast, computers are also accurate. Errors that may occur can almost

always be attributed to human error (inaccurate data, poorly designed system or faulty

instructions/programs written by the programmer). The computers are the accurate

machine that can perform large number of tasks without errors, but if we feed wrong

data to the computer it returns the same wrong information called GIGO(Garbage in

Garbage Out).

Diligence

Unlike human beings, computers are highly consistent. They do not suffer from human

traits of boredom and tiredness resulting in lack of concentration. Computers,

therefore, are better than human beings in performing voluminous and repetitive jobs.

Versatility

Computers are versatile machines and are capable of performing any task as long as it

can be broken down into a series of logical steps. The presence of computers can be

seen in almost every sphere j Railway/Air reservation, Banks, Hotels, Weather

forecasting and many more.

Storage

Capacity Today’s computers can store large volumes of data. A piece of information

once recorded (or stored) in the computer, can never be forgotten and can be retrieved

Computer Hardware and Architecture 3

almost instantaneously. The storage capacity of computer is measured in terms of

kilobyte(KB) Megabyte(MB)k Gigabyte(GB), and Terabyte(TB).

Basic Unit of storage

Collection of 8 bits = 1 BYTE

1024 bytes = 1 Kilo Bytes (KB)

1024 Kilo bytes = 1 Mega Bytes (MB)

1024 Megabytes = 1 Giga Bytes (GB)

1024 Giga bytes = 1 Tera Bytes (TB)

1.2 History of Computers and its Generation

The first counting device was used by the primitive people. They used sticks, stones

and bones as counting tools. As human mind and technology improved with time more

computing devices were developed. Some of the popular computing devices starting

with the first to recent ones are described below;

Abacus

The history of computer begins with the birth of abacus which is believed to be the

first computer. It is said that Chinese invented Abacus around 4,000 years ago.It was

a wooden rack which has metal rods with beads mounted on them. The beads were

moved by the abacus operator according to some rules to perform arithmetic

calculations. Abacus is still used in some countries like China, Russia and Japan. An

image of this tool is shown below;

Fig. Abacus

4 Computer Hardware and Architecture

Napier's Bones

It was a manually-operated calculating device which was invented by John Napier

(1550-1617) of Merchiston. In this calculating tool, he used 9 different ivory strips or

bones marked with numbers to multiply and divide. So, the tool became known as

"Napier's Bones. It was also the first machine to use the decimal point

Fig. Napier Bone

Pascaline

Pascaline is also known as Arithmetic Machine or Adding Machine. It was invented

between 1642 and 1644 by a French mathematician-philosopher Biaise Pascal. It is

believed that it was the first mechanical and automatic calculator.Pascal invented this

machine to help his father, a tax accountant. It could only perform addition and

subtraction. It was a wooden box with a series of gears and wheels. When a wheel is

rotated one revolution, it rotates the neighboring wheel. A series of windows is given

on the top of the wheels to read the totals. An image of this tool is shown below;

Fig. Pascaline

Computer Hardware and Architecture 5

Stepped Reckoner or Leibnitz wheel

It was developed by a German mathematician-philosopher Gottfried Wilhelm Leibnitz

in 1673. He improved Pascal's invention to develop this machine. It was a digital

mechanical calculator which was called the stepped reckoner as instead of gears it was

made of fluted drums. See the following image;

Tabulating Machine

It was invented in 1890, by Herman Hollerith, an American statistician. It was a

mechanical tabulator based on punch cards. It could tabulate statistics and record or

sort data or information. This machine was used in the 1890 U.S. Census. Hollerith

also started the Hollerith? Tabulating Machine Company which later became

International Business Machine (IBM) in 1924.

Fig.Tabulating Machine

THE BABBAGE ENGINE

6 Computer Hardware and Architecture

Charles Babbage (1791-1871), computer pioneer, designed the first automatic

computing engines. He invented computers but failed to build them. The first complete

Babbage Engine was completed in London in 2002, 153 years after it was designed

Difference Engine

In the early 1820s, it was designed by Charles Babbage who is known as "Father of

Modern Computer". It was a mechanical computer which could perform simple

calculations. It was a steam driven calculating machine designed to solve tables of

numbers like logarithm tables.

Analytical Engine

This calculating machine was also developed by Charles Babbage in 1830. It was a

mechanical computer that used punch-cards as input. It was capable of solving any

mathematical problem and storing information as a permanent memory.

Computer Hardware and Architecture 7

Ada Lovelace

Lovelace collaborated with inventor Charles Babbage on his general purpose

computing machine, the Analytical Engine, which is considered to be the first

published algorithm developed specifically to be used on a computer.2. In 1843, she

published what we would now call a computer program to generate Bernoulli

numbers. Though Babbage had written fragments of programs before, Lovelace's was

the most complete, most elaborate and the first published.

ELECTROMECHANICAL COMPUTERS :

In the early part of twentieth century, tabulating machines were growing rapidly.

Meanwhile, the computational need of the nations was also increasing. So,

governments, universities, and research organizations were trying to find the solution

to meet those needs.In 1984, next important event occurred in history. The

8 Computer Hardware and Architecture

electromechanicalcomputer was born with the development of MARK I by Howard

Aiken and other was constructed MARK I at Harvard University under the

sponsorship of IBM (International Business Machine).The MARK I also known as the

Automatic Sequence Controlled Calculator. It was 50ft. long and 8ft. high. It used

electronic tubes and electrical relays.MARK I took 41/2seconds to multiply two 23 digit

numbers. It was able to produce ballistics tables that were used in connection with

Second World War. The input device used was the punched paper tape.

ELECTRONIC COMPUTERS

The age of electronic computer began after 1890 when vacuum tubes were introduced.

Such tubes were thousands of times faster than the earlier electromechanical

devices.The first electronic digital computer was developed by John V. Attansofft and

his student Clifford Berry. It was called Attansoff-Berry Computer (ABC computer).

ABC computer used vacuum tubes (electronic device) instead of electromechanical

relays. It was comparatively very fast as compared to the previous computers.ABC

computer could not become popular because it could solve only certain type of

problem and it used advanced electronic technology of that time.

Generation of Computer:

Generation in computer terminology is a change in technology a computer is/was being

used. Initially, the generation term was used to distinguish between varying hardware

technologies. Nowadays, generation includes both hardware and software, which

together make up an entire computer system.There are five computer generations

known till date. Each generation has been discussed in detail along with their time

period and characteristics. In the following table, approximate dates against each

generation has been mentioned, which are normally accepted.Following are the main

five generations of computers.

 First Generation

 Second Generation

 Third Generation

 Fourth Generation

 Fifth Generation

Computer Hardware and Architecture 9

First Generation Computer

The period of first generation was from 1946-1959. The computers of first generation

used vacuum tubes as the basic components for memory and circuitry for CPU (Central

Processing Unit). These tubes, like electric bulbs, produced a lot of heat and the

installations used to fuse frequently. Therefore, they were very expensive and only

large organizations were able to afford it.In this generation, mainly batch processing

operating system was used. Punch cards, paper tape, and magnetic tape was used as

input and output devices. The computers in this generation used machine code as the

programming language.

The main features of the first generation are −

 Vacuum tube technology

 Unreliable

 Supported machine language only

 Very costly

 Generated a lot of heat

 Slow input and output devices

 Huge size

 Need of AC

 Non-portable

10 Computer Hardware and Architecture

 Consumed a lot of electricity

Some computers of this generation were −

 ENIAC

 EDVAC

 UNIVAC

 IBM-701

 IBM-650

Second Generation Computer

The period of second generation was from 1959-1965. In this generation, transistors

were used that were cheaper, consumed less power, more compact in size, more

reliable and faster than the first generation machines made of vacuum tubes. In this

generation, magnetic cores were used as the primary memory and magnetic tape and

magnetic disks as secondary storage devices.In this generation, assembly language and

high-level programming languages like FORTRAN, COBOL were used. The

computers used batch processing and multiprogramming operating system.

The main features of second generation are −

 Use of transistors

 Reliable in comparison to first generation computers

 Smaller size as compared to first generation computers

 Generated less heat as compared to first generation computers

 Consumed less electricity as compared to first generation computers

Computer Hardware and Architecture 11

 Faster than first generation computers

 Still very costly

 AC required

 Supported machine and assembly languages

Some computers of this generation were −

 IBM 1620

 IBM 7094

 CDC 1604

 CDC 3600

 UNIVAC 1108

Third Generation Computer

The period of third generation was from 1965-1971. The computers of third generation

used Integrated Circuits (ICs) in place of transistors. A single IC has many transistors,

resistors, and capacitors along with the associated circuitry.The IC was invented by

Jack Kilby. This development made computers smaller in size, reliable, and efficient.

In this generation remote processing, time-sharing, multiprogramming operating

system were used. High-level languages (FORTRAN-II TO IV, COBOL, PASCAL

PL/1, BASIC, ALGOL-68 etc.) were used during this generation.

The main features of third generation are

 IC used

 More reliable in comparison to previous two generations

 Smaller size

 Generated less heat

 Faster

12 Computer Hardware and Architecture

 Lesser maintenance

 Costly

 AC required

 Consumed lesser electricity

 Supported high-level language

Some computers of this generation were −

 IBM-360 series

 Honeywell-6000 series

 PDP (Personal Data Processor)

 IBM-370/168

 TDC-316

Fourth Generation Computer

The period of fourth generation was from 1971-1980. Computers of fourth generation

used Very Large Scale Integrated (VLSI) circuits. VLSI circuits having about 5000

transistors and other circuit elements with their associated circuits on a single chip

made it possible to have microcomputers of fourth generation.Fourth generation

computers became more powerful, compact, reliable, and affordable. As a result, it

gave rise to Personal Computer (PC) revolution. In this generation, time sharing, real

time networks, distributed operating system were used. All the high-level languages

like C, C++, DBASE etc., were used in this generation.

The main features of fourth generation are −

 VLSI technology used

 Very cheap

Computer Hardware and Architecture 13

 Portable and reliable

 Use of PCs

 Very small size

 Pipeline processing

 No AC required

 Concept of internet was introduced

 Great developments in the fields of networks

 Computers became easily available

Some computers of this generation were −

 DEC 10

 STAR 1000

 PDP 11

 CRAY-1(Super Computer)

 CRAY-X-MP(Super Computer)

Fifth Generation Computer

The period of fifth generation is 1980 to till date. In the fifth generation, VLSI

technology became ULSI (Ultra Large Scale Integration) technology, resulting in the

production of microprocessor chips having ten million electronic components.This

generation is based on parallel processing hardware and AI (Artificial Intelligence)

software. AI is an emerging branch in computer science, which interprets the means

and method of making computers think like human beings. All the high-level

languages like C and C++, Java, .Net etc., are used in this generation.

14 Computer Hardware and Architecture

AI includes −

 Robotics

 Neural Networks

 Game Playing

 Development of expert systems to make decisions in real-life situations

 Natural language understanding and generation

The main features of fifth generation are −

 ULSI technology

 Development of true artificial intelligence

 Development of Natural language processing

 Advancement in Parallel Processing

 Advancement in Superconductor technology

 More user-friendly interfaces with multimedia features

 Availability of very powerful and compact computers at cheaper rates

Some computer types of this generation are −

 Desktop

 Laptop

 Notebook

 Ultrabook

 Chromebook

Computer Hardware and Architecture 15

Importance and Application of computer in 21st Century

Computer is a device through which you can perform a variety of jobs. You can use

your computer system for different applications by changing the software packages.

Here are the list of uses or applications of computer:

 Scientific research

 Business application

 Education

 Entertainment

 Banks

 Communication

 Engineering

 Medicine

 Book Publishing

 Games

 Personal

 Accounting

For Scientific Research

Scientific research was the first application of computer as computer was first used to

perform this job that is scientific research. At that time to now, the speed and accuracy

of computer enabled scientific analysis carried out too fast.Computer controlled robots

must be used in all those areas where there is danger to human being such as in nuclear

research and deep sea investigation etc.

For Business Application

Computer can also be used for the purpose of business.

Through computer, companies can grow their business as fast as possible through

quick analysis of their previous project on the computer screen (according to the data

feeded inside) and deciding what to do next without any delay.As from individual to

multinational companies, all are using computer for business purpose like keeping

account information, stocks, prices, items etc.

16 Computer Hardware and Architecture

For Education

You can also use your computer system to educate yourself through audio, videos or

images etc.Now-a-days, there are thousands of websites available over Internet that

are ready to deliver education for free in almost every subjects.You can choose

whether you want to learn online or offline. In online learning, you can open any

website to read your desired topic while in offline learning you can learn through

videos, PDFs photos etc., all these documents can be downloaded through internet.

For Entertainment

Most of the persons are using computer for entertainment purposes such as:

 watching movies

 watching videos

 listening songs

 photos

 animations etc.

Computer can be used to create these things in an attractive manner so that user loves

to enjoy the things.

In Banks

Banks are the place where there is continuous uses of computer or we can says that

banks are the major users of computers. For example, ATM (Automated teller

machine) is used where we are free to either deposit or withdraw our cash in/from our

Bank.In banks, all information such as account holders detail, deposits, withdrawal,

interest, etc. are managed by computers.Banks are also using computer network to

interconnect all of its branches so that their users feel always free to deposit his or her

money in any branch of the same bank.

For Communication

Using your computer system for the purpose of communication gives you a lot of

benefits. For example, if you will use email to send message or anything to your friends

or any of your contacts, then you don't have to use pen and paper to write and take that

paper to post office and then postman will deliver that later after some or few days that

Computer Hardware and Architecture 17

will not good if you want to send any urgent information to the same person.Therefore,

using email, you can also saves your time and cost to deliver any information very fast.

You only need a computer and internet connectivity.Now-a-days, peoples are using

chat message, email, voice-mail etc. for communication purpose.You can also use

computer to communicate through direct video conference with your contacts/friends

present at any place without any cost except internet connectivity.Now you have got

enough idea about communication through computer. It's time to move on another

application of computer which is engineering.

For Engineering Purposes

Computer are also using for the purpose of Engineering, that is, to design any machine

without actually making it through CAD (Computer aided design) softwares and once

the design is accepted, and then using CAM (Computer aided manufacturing) process

company can produce a large number of such products at very fast speed.Architects

are also using computers to draw and design individual houses to big buildings like

Apartments. There are a lot more uses of computer for engineering purposes.

For Medicines Related

Computer plays an important role in medical field also. For example in ICU (Intensive

Care Unit) chamber in hospital, computer keeps track of each and everything going

inside the patient's body such as blood pressure and Heartbeat etc.Keeping record of

patients and medicines are also becomes easy through the use of Computer. Computer

also plays an important role to perform CT (Computed tomography) scan and X-Ray

of patients to give the scanned object of specified area of patient's body in the form of

graphics like images.

For Book Publishing

Book publishing becomes an easy task with the use of computer.Book publishers are

now using DTP (Desktop publishing) software like MS-Word to publish their books.

For Games

Now-a-days, peoples are using computers most of the time to play games.For online

games to play, you must have the internet connectivity whereas for offline games, you

can start without any internet connectivity.There are a variety of games available in

18 Computer Hardware and Architecture

computer world. Here are some of the category available in the game field:

 action

 racing

 adventurous

 puzzle

 simulations

 combat etc.

Peoples are playing (mostly today's or new generation childs) games on computer for

few to many hours.

Some popular games are listed here:

 Minecraft

 Counter Strike

 PubG

 WoW

 Grand Theft Auto

 Skyrim

 Angry Bird

 Call of Duty

 Halo

 Pokemon

 Super Mario Bros etc.

For Personal Use

Computer can also be used for personal purposes. One can use computer system to

keep all day-to-day details that are essential to keep anywhere.You can use it for

personal things such as investments, incomes, expenditures, savings etc.For

Accounting PurposesComputers are highly used for accounting purposes to handle

company financial accounts and inventory management using some accounting

software like Tally.With the use of computer, the task of maintaining accounts become

very easy. Later you can also retrieve the data on the basis of various pattern or

Computer Hardware and Architecture 19

requirement very easily

1.4 Computer Organization:

Von Neumann Architecture

Von Neumann architecture was first published by John Von Neumann in 1945. His

computer architecture design consists of a Control Unit, Arithmetic and Logic

Unit (ALU), Memory Unit, Registers and Inputs/Outputs. Von Neumann architecture

is based on the stored-program computer concept, where instruction data and program

data are stored in the same memory. This design is still used in most computers

produced today.

Fig .Von Neumann Architecture

Central Processing Unit (CPU)

The Central Processing Unit (CPU) is the electronic circuit responsible for executing

the instructions of a computer program.

Central Processing Unit (CPU)

The Central Processing Unit (CPU) is the electronic circuit responsible for executing

the instructions of a computer program. It is sometimes referred to as the

microprocessor or processor. The CPU contains the ALU, CU and a variety

of registers.

20 Computer Hardware and Architecture

Registers

Registers are high speed storage areas in the CPU. All data must be stored

in register before it can be processed.

Arithmetic and Logic Unit (ALU)

The ALU allows arithmetic (add, subtract etc) and logic (AND, OR, NOT etc)

operations to be carried out. It also performs clear and shift operation.

Control Unit (CU)

The control unit controls the operation of the computer’s ALU, memory and

input/output devices, telling them how to respond to the program instructions it has

just read and interpreted from the memory unit.The control unit also provides the

timing and control signals required by other computer components.

Topics / Hardware and Software / Von Neumann Architecture

Von Neumann Architecture

Central Processing Unit (CPU)

The Central Processing Unit (CPU) is the electronic circuit responsible for executing

the instructions of a computer program. It is sometimes referred to as

themicroprocessor or processor. The CPU contains the ALU, CU and a variety

of registers.

Registers

Registers are high speed storage areas in the CPU. All data must be stored

in register before it can be processed.

Arithmetic and Logic Unit (ALU)

The ALU allows arithmetic (add, subtract etc) and logic (AND, OR, NOT etc)

operations to be carried out.

Control Unit (CU)

The control unit controls the operation of the computer’s ALU, memory and

input/output devices, telling them how to respond to the program instructions it has

just read and interpreted from the memory unit.The control unit also provides the

timing and control signals required by other computer components.

Computer Hardware and Architecture 21

Buses

Buses are the means by which data is transmitted from one part of a computer to

another, connecting all major internal components to the CPU and memory.A standard

CPU system bus is comprised of a control bus, data bus and address bus.

Address Bus Carries the addresses of data (but not the data) between the processor

and memory

Data Bus Carries data between the processor, the memory unit and the

input/output devices

Control Bus Carries control signals/commands from the CPU (and status signals

from other devices) in order to control and coordinate all the

activities within the computer

Memory Unit

The memory unit consists of RAM, sometimes referred to as primary or main

memory. Unlike a hard drive (secondary memory), this memory is fast and also

directly accessible by the PU.RAM is split into partitions. Each partition consists of

an address and its contents (both n binary form).The address will uniquely identify

every location in the memory.Loading data from permanent memory (hard drive), into

the faster and directly accessible temporary memory (RAM), allows the CPU to

operate much quicker.

Input / Output Devices:

These devices are used to enter information and instructions into a computer for

storage or processing and to deliver the processed data to a user. Input/Output devices

are required for users to communicate with the computer. In simple terms, input

devices bring information INTO the computer and output devices bring information

OUT of a computer system. These input/output devices are also known as peripherals

since they surround the CPU and memory of a computer system

22 Computer Hardware and Architecture

Fig. Input and output devices

Input Devices

An input device is any device that provides input to a computer. There are many input

devices, but the two most common ones are a keyboard and mouse. Every key you

press on the keyboard and every movement or click you make with the mouse sends a

specific input signal to the computer.

Keyboard

The keyboard is very much like a standard typewriter keyboard with a few additional

keys. The basic QWERTY layout of characters is maintained to make it easy to use

the system. The additional keys are included to perform certain special functions.

These are known as function keys that vary in number from keyboard to keyboard.

Mouse

A device that controls the movement of the cursor or pointer on a display screen. A

Computer Hardware and Architecture 23

mouse is a small object you can roll along a hard and flat surface (see in Fig). Its name

is derived from its shape, which looks a bit like a mouse. As you move the mouse, the

pointer on the display screen moves in the same direction.

Fig. Optical Mouse

Trackball

A trackball is an input device used to enter motion data into computers or other

electronic devices. It serves the same purpose as a mouse, but is designed with a

moveable ball on the top, which can be rolled in any direction.

Touchpad

A touch pad is a device for pointing (controlling input positioning) on a computer

display screen. It is an alternative to the mouse. Originally incorporated in laptop

computers, touch pads are also being made for use with desktop computers. A touch

pad works by sensing the user’s finger movement and downward pressure.

24 Computer Hardware and Architecture

Touch Screen

It allows the user to operate/make selections by simply touching the display screen. A

display screen that is sensitive to the touch of a finger or stylus. Widely used on ATM

machines, retail point-of-sale terminals, car navigation systems, medical monitors and

industrial control panels and modern mobile phones.

Light Pen

Light pen is an input device that utilizes a light-sensitive detector to select objects on

a display screen. (Fig. )

Magnetic ink character recognition (MICR):

MICR can identify character printed with a special ink that contains particles of

magnetic material. This device particularly finds applications in banking industry.

Computer Hardware and Architecture 25

Optical mark recognition (OMR)

Optical mark recognition, also called mark sense reader is a technology where an OMR

device senses the presence or absence of a mark, such as pencil mark. OMR is widely

used in tests such as aptitude test.

Bar code reader

Bar-code readers are photoelectric scanners that read the bar codes or vertical zebra

strips marks, printed on product containers. These devices are generally used in super

markets, bookshops etc.

Scanner

Scanner is an input device that can read text or illustration printed on paper and

translates the information into a form that the computer can use. A scanner works by

digitizing an image. (Fig. )

26 Computer Hardware and Architecture

Output Devices

Output device receives information from the CPU and presents it to the user in the

desired from. The processed data, stored in the memory of the computer is sent to the

output unit, which then converts it into a form that can be understood by the user. The

output is usually produced in one of the two ways – on the display device, or on paper

(hard copy).

Monitor

is often used synonymously with “computer screen” or “display.” Monitor is an output

device that resembles the television screen . It may use a Cathode Ray Tube (CRT) to

display information. The monitor is associated with a keyboard for manual input of

characters and displays the information as it is keyed in. It also displays the program

or application output. Like the television, monitors are also available in different sizes.

Fig. LCD Monitor

Printer

Printers are used to produce paper (commonly known as hardcopy) output. Based on

the technology used, they can be classified as Impact or Non-impact printers. Impact

printers use the typewriting printing mechanism wherein a hammer strikes the paper

through a ribbon in order to produce output. Dot-matrix and Character printers fall

under this category. Non-impact printers do not touch the paper while printing. They

use chemical, heat or electrical signals to etch the symbols on paper. Inkjet, Deskjet,

Laser, Thermal printers fall under this category of printers.

Computer Hardware and Architecture 27

Fig: Laser Printer

Plotter

Plotters are used to print graphical output on paper. It interprets computer commands

and makes line drawings on paper using multi colored automated pens. It is capable of

producing graphs, drawings, charts, maps etc.Fig. Plotter)

Fig. Plotter

Facsimile (FAX)

Facsimile machine, a device that can send or receive pictures and text over a telephone

line. Fax machines work by digitizing an image.

Sound cards and Speaker(s)

An expansion board that enables a computer to manipulate and output sounds. Sound

cards are necessary for nearly all CD-ROMs and have become commonplace on

modern personal computers. Sound cards enable the computer to output sound through

speakers connected to the board, to record sound input from a microphone connected

to the computer, and manipulate sound stored on a disk.

28 Computer Hardware and Architecture

Power Supply

Abbreviated as PS or P/S, a power supply or PSU (power supply unit) is

a hardware component of a computer that supplies all other components with power.

The power supply converts a 110-115 or 220-230 volt AC (alternating current) into a

steady low-voltage DC (direct current) usable by the computer and rated by the

number of watts it generates. The image shows True 330, a 330 Watt power

supply.While the computer is on the fan(s) inside a power supply should always be

running. If the fan is not running (spinning), either the computer is not working or the

fan inside the power supply has failed and the power supply should be replaced.

Computer case

A computer case, also known as a computer chassis, tower, system unit, CPU (when

referring to the case as a whole rather than the processor), or cabinet, is the enclosure

that contains most of the components of a personal computer (usually excluding the

display, keyboard, and mouse). Cases are usually constructed from steel (often

SECC—steel, electrogalvanized, cold-rolled, coil) or aluminum. Plastic is sometimes

used, and other materials such as glass, wood and even Lego bricks have appeared in

home-built cases.

Motherboard: Motherboard is alternatively referred to as the mb, mainboard, mboard,

mobo, mobd, backplane board, base board, main circuit board, planar board, system

Computer Hardware and Architecture 29

board, or a logic board on Apple computers. The motherboard is a printed circuit

board and foundation of a computer that is the biggest board in a computer chassis. It

allocates power and allows communication to and between the CPU, RAM, and all

other computer hardware components.

A motherboard provides connectivity between the hardware components of a

computer, like the processor (CPU), memory (RAM), hard drive, and video card.

There are multiple types of motherboards, designed to fit different types and sizes of

computers.Each type of motherboard is designed to work with specific types of

processors and memory, so they are not capable of working with every processor and

type of memory. However, hard drives are mostly universal and will work with the

majority of motherboards, regardless of the type or brand.

Central Processing Unit

Alternately referred to as a processor, central processor, or microprocessor, the CPU

(pronounced sea-pea-you) is the central processing unit of the computer. A computer's

CPU handles all instructions it receives from hardware and software running on the

computer.CPUs are built by placing billions of microscopic transistors onto a single

computer chip. Those transistors allow it to make the calculations it needs to run

programs that are stored on your system’s memory. One of the most common

advancements of CPU technology is in making those transistors smaller and smaller.

That’s resulted in the improvement to CPU speed over the decades, often referred to

as Moore’s Law.

Central Processing Unit (CPU) consists of the following features

 CPU is considered as the brain of the computer.

30 Computer Hardware and Architecture

 CPU performs all types of data processing operations.

 It stores data, intermediate results, and instructions (program).

 It controls the operation of all parts of the computer.

Over the history of computer processors, the speed (clock speed) and capabilities of

the processor have dramatically improved. For example, the first microprocessor was

the Intel 4004 that was released on November 15, 1971, and had 2,300 transistors and

performed 60,000 operations per second. The Intel Pentium processor has 3,300,000

transistors and performs around 188,000,000 instructions per second.

Types of CPUs

In the past, computer processors used numbers to identify the processor and help

identify faster processors. For example, the Intel 80486 (486) processor is faster than

the 80386 (386) processor. After the introduction of the Intel Pentium processor

(which would technically be the 80586), all computer processors started using names

like Athlon, Duron, Pentium, and Celeron. Today, in addition to the different names

of computer processors, there are different architectures (32-bit and 64-bit), speeds,

and capabilities. Below is a list of the more common types of CPUs for home or

business computers.

CPU itself has following three components.

 Memory or Storage Unit

 Control Unit

Computer Hardware and Architecture 31

 ALU(Arithmetic Logic Unit)

Memory or Storage Unit

This unit can store instructions, data, and intermediate results. This unit supplies

information to other units of the computer when needed. It is also known as internal

storage unit or the main memory or the primary storage or Random Access Memory

(RAM).Its size affects speed, power, and capability. Primary memory and secondary

memory are two types of memories in the computer. Functions of the memory unit are:

 It stores all the data and the instructions required for processing.

 It stores intermediate results of processing.

 It stores the final results of processing before these results are released to an

output device.

 All inputs and outputs are transmitted through the main memory.

Control Unit

This unit controls the operations of all parts of the computer but does not carry out any

actual data processing operations.

Functions of this unit are −

 It is responsible for controlling the transfer of data and instructions among other

units of a computer.

 It manages and coordinates all the units of the computer.

 It obtains the instructions from the memory, interprets them, and directs the

operation of the computer.

 It communicates with Input/Output devices for transfer of data or results from

storage.

 It does not process or store data.

ALU (Arithmetic Logic Unit)

This unit consists of two subsections namely,

 Arithmetic Section

 Logic Section

32 Computer Hardware and Architecture

Arithmetic Section

Function of arithmetic section is to perform arithmetic operations like addition,

subtraction, multiplication, and division. All complex operations are done by making

repetitive use of the above operations.

Logic Section

Function of logic section is to perform logic operations such as comparing, selecting,

matching, and merging of data.

Chipset: A chipset is a set of electronic components on an integrated circuit that

manages the transfer of data between the CPU, RAM, storage, and I/O devices. The

first chipset, the 82C206, was introduced in 1986 by Chips and Technologies. The

original 82C206 chipset included the 82284 clock generator functions, 82288 bus

controller, 8254 system timer, dual 8259 interrupt controllers, dual 8237 DMA

controllers, and the MC146818 clock. Four of the 82C206 chips were later replaced

by CS8221 or NEAT (New Enhanced AT) chipset that contained only three chips. This

chipset was then replaced by the 82C836 SCAT (single-chip AT) chipset that

combined all the chips in the set into one chip.

Examples of chipset manufacturers include ALi, AMD, Intel, NVidia, SiS, and VIA.

These chipsets can include instructions that help control the CPU, PCI, ISA,

or USB hardware. They are often divided into a multitiered architecture referred to

as North bridge and South bridge, as well as a Super I/O chip. An example of a recent

Intel chipset is the i820 or the Intel 820 chipset.

Fig. Chipset

Computer Hardware and Architecture 33

Real- Time Clock(RTC)

A real-time clock (RTC) is a computer clock, usually in the form of an integrated

circuit that is solely built for keeping time. Naturally, it counts hours, minutes, seconds,

months, days and even years. RTCs can be found running in personal computers,

embedded systems and servers, and are present in any electronic device that may

require accurate time keeping. Being able to still function even when the computer is

powered down through a battery or independently from the system’s main power is

fundamental.

RTCs must accurately keep time, even when the device is powered off because, it is

often used as a trigger for turning the device on or triggering events such as alarm

clocks. RTC ICs run on an alternate power source, which allows it to continually

operate under low power or even when the computer is turned off. ICs on older systems

utilize lithium batteries, whereas newer systems make use of auxiliary batteries or

supercapacitors. RTC ICs that use supercapacitors are rechargeable and can be

soldered. But in most consumer-grade motherboards, the RTC is powered by a single

battery that, when removed, resets the RTC to its starting point.

Fig.RTC

BIOS (Basic Input Ourtput System)

Short for Basic Input/Output System, the BIOS (pronounced bye-oss) is a ROM chip

found on motherboards that allows you to access and set up your computer system at

the most basic level. The picture below is an example of what a BIOS chip may look

like on a computer motherboard. The example picture below is of an early AMIBIOS,

a type of BIOS manufactured by AMI.The BIOS includes instructions on how to load

basic computer hardware. It also includes a test referred to as a POST (Power-On Self-

Test) that helps verify the computer meets requirements to boot up properly. If the

computer does not pass the POST, you will receive a combination of beeps indicating

34 Computer Hardware and Architecture

what is malfunctioning in the computer.

Fig. BIOS interface

The four main functions of a PC BIOS

 POST - Test the computer hardware and make sure no errors exist before

loading the operating system. Additional information on the POST is available

on our POST and beep codes page.

 Bootstrap Loader - Locate the operating system. If a capable operating system is

located, the BIOS will pass control to it.

 BIOS drivers - Low-level drivers that give the computer basic operational

control over your computer's hardware.

 BIOS setup or CMOS setup - Configuration program that allows you to

configure hardware settings including system settings such as computer

passwords, time, and date.

Computer Ports:

A port is a physical docking point using which an external device can be connected to

the computer. It can also be programmatic docking point through which information

flows from a program to the computer or over the Internet.

Characteristics of Ports

A port has the following characteristics:

 External devices are connected to a computer using cables and ports.

 Ports are slots on the motherboard into which a cable of external device is

Computer Hardware and Architecture 35

plugged in.

 Examples of external devices attached via ports are the mouse, keyboard,

monitor, microphone, speakers, etc

Serial Port

 Used for external modems and older computer mouse

 Two versions: 9 pin, 25 pin model

 Data travels at 115 kilobits per second

Parallel Port

 Used for scanners and printers

 Also called printer port

 25 pin model

 IEEE 1284-compliant Centronics port

PS/2 Port

 Used for old computer keyboard and mouse

 Also called mouse port

 Most of the old computers provide two PS/2 port, each for the mouse and

keyboard

 IEEE 1284-compliant Centronics port

Universal Serial Bus (or USB) Port

 It can connect all kinds of external USB devices such as external hard disk,

printer, scanner, mouse, keyboard, etc.

 It was introduced in 1997.

 Most of the computers provide two USB ports as minimum.

 Data travels at 12 megabits per seconds.

 USB compliant devices can get power from a USB port.

VGA Port

 Connects monitor to a computer's video card.

 It has 15 holes.

36 Computer Hardware and Architecture

 Similar to the serial port connector. However, serial port connector has pins,

VGA port has holes.

Power Connector

 Three-pronged plug.

 Connects to the computer's power cable that plugs into a power bar or wall

socket.

Firewire Port

 Transfers large amount of data at very fast speed.

 Connects camcorders and video equipment to the computer.

 Data travels at 400 to 800 megabits per seconds.

 Invented by Apple.

 It has three variants: 4-Pin FireWire 400 connector, 6-Pin FireWire 400

connector, and 9-Pin FireWire 800 connector.

Modem Port

 Connects a PC's modem to the telephone network.

Ethernet Port

 Connects to a network and high speed Internet.

 Connects the network cable to a computer.

 This port resides on an Ethernet Card.

 Data travels at 10 megabits to 1000 megabits per seconds depending upon the

network bandwidth.

Game Port

 Connect a joystick to a PC

 Now replaced by USB

Digital Video Interface, DVI port

 Connects Flat panel LCD monitor to the computer's high-end video graphic

cards.

 Very popular among video card manufacturers.

Computer Hardware and Architecture 37

Sockets

 Sockets connect the microphone and speakers to the sound card of the computer.

Hardware Interface:An interface is a physical device, port, or connection that interacts

with the computer or other hardware device. For example, IDE is a disk drive interface

for computer hard drives and ATAPI is an interface for CD-ROM drives.

Different Types of Interfaces

IDE interfaces

Integrated Drive Electronics (IDE) is a standard interface for connecting a

motherboard to storage devices such as hard drives and CD-ROM/DVD drives. The

original IDE had a 16-bit interface that connected two devices to a single-ribbon cable.

This cost-effective IDE device carried its own circuitry and included an integrated disk

drive controller. Prior to IDE, controllers were separate external devices.

SATA Interface

The SATA drive is a pair of flat connectors – the larger one for power, and the smaller

one for data. SATA is an acronym for Serial Advanced Technology Attachment,

often shortened to Serial ATA. Serial refers to the fact that data is sent one bit at a time

down a single connection in each direction. There’s a separate connection for data

going in to and out of the device. SATA interfaces can transmit up to 150, 300, or 600

megabytes per second, depending on the version of the interface being used.

Fig. SATA Interfaces

SATA cables

38 Computer Hardware and Architecture

PATA Interface:

The PATA drive uses the larger connector full of pins for data, and the four-prong

connector on the right for power. PATA is an acronym for Parallel Advanced

Technology Attachment, often shortened to Parallel ATA. Parallel refers to the fact

that data is sent 16 bits at a time through a single 16-bit connection, which is used for

data traveling in both directions.

PATA actually transfers data more slowly, for a variety of reasons. Current PATA

interfaces can transfer at up to 133 megabytes per second

Fig. PATA interface

Fig. PATA Cable

Computer Hardware and Architecture 39

References:

https://www.javatpoint.com/von-neumann-model

https://www.computerscience.gcse.guru/theory/von-neumann-architecture

https://www.computerhope.com/jargon/p/power-supply.htm

https://www.tutorialspoint.com/computer_fundamentals/computer_ports.htm

40 Computer Hardware and Architecture

UNIT 2

Computer Memory

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

2.1 Characteristics of Memory System

Computer memory is a generic term for all of the different types of data storage

technology that a computer may use, including RAM, ROM, and flash memory. Some

types of computer memory are designed to be very fast, meaning that the central

processing unit (CPU) can access data stored there very quickly. Other types are

designed to be very low cost, so that large amounts of data can be stored there

economically. Another way that computer memory can vary is that some types

are non-volatile, which means they can store data on a longterm basis even when there

is no power. And some types are volatile, which are often faster, but which lose all the

data stored on them as soon as the power is switched off. A computer system is built

using a combination of these types of computer memory, and the exact configuration

can be optimized to produce the maximum data processing speed or the minimum cost,

or some compromise between the two.

2.2 The memory of the computer is divided into two categories:

1. Primary Memory

2. Secondary Memory

2.2.1 Primary Memory

This is the main memory of the computer. CPU can directly read or write on this

memory. It is fixed on the motherboard of the computer.

Primary memory is further divided in two types:

1. RAM(Random Access Memory)

2. ROM(Read Only Memory)

Computer Hardware and Architecture 41

RAM (Random Access Memory)

RAM is a temporary memory. The information stored in this memory is lost as the

power supply to the computer is turned off. That’s why it is also called Volatile

Memory. It stores the data and instruction given by the user and also the results

produced by the computer temporarily.

There are two types of RAM

 Static RAM

 Dynamic RAM

Static RAM

Static Random Access Memory (Static RAM or SRAM) is a type of RAM that holds

data in a static form, that is, as long as the memory has power. Unlike dynamic RAM,

it does not need to be refreshed.SRAM stores a bit of data on four transistors using two

cross-coupled inverters. The two stable states characterize 0 and 1. During read and

write operations another two access transistors are used to manage the availability to

a memory cell. To store one memory bit it requires six metal-oxide-semiconductor

field-effect transistors (MOFSET). MOFSET is one of the two types of SRAM chips;

the other is the bipolar junction transistor. The bipolar junction transistor is very fast

but consumes a lot of energy. MOFSET is a popular SRAM type.

42 Computer Hardware and Architecture

SRAM are comparatively fast (5- 20ns). Above figure is digital logic view it uses some

wires, some gates and some D-latches

Dyanamic Random Access Memory(DRAM)

Dynamic random access memory, or DRAM, is a specific type of random access

memory that allows for higher densities at a lower cost. The memory modules found

in laptops and desktops use DRAM. DRAM use a single transistor to store a

bit. It is slower than SRAM typically 50ns-100ns. It was invented by Robert

Dennard in 1966 at IBM, DRAM works much differently than other types of memory.

The fundamental storage cell within DRAM is composed of two elements: a transistor

and a capacitor.

When a bit needs to be put in memory, the transistor is used to charge or discharge the

capacitor. A charged capacitor represents a logic high, or '1', while a discharged

capacitor represents a logic low, or '0'. The charging/discharging is done via the word

line and bit line, shown in Figure .

Computer Hardware and Architecture 43

ROM(Readonly Memory)

Information stored in ROM is permanent in naturei.e., it holds the data even if the

system is switched off. It holds the starting instructions for the computer. ROM cannot

be overwritten by the computer. It is also called Non-Volatile Memory.

Read-only memory (ROM) is a type of storage medium that permanently stores data

on personal computers (PCs) and other electronic devices. It contains the programming

needed to start a PC, which is essential for boot-up; it performs major input/output

tasks and holds programs or software instructions.Because ROM is read-only, it cannot

be changed; it is permanent and non-volatile, meaning it also holds its memory even

when power is removed. By contrast, random access memory (RAM) is volatile; it is

lost when power is removed.

There are numerous ROM chips located on the motherboard and a few on expansion

boards. The chips are essential for the basic input/output system (BIOS), boot up,

reading and writing to peripheral devices, basic data management and the software for

basic processes for certain utilities.

Different types of ROM memory

 PROM (Programmable Read Only Memory): is read-only memory that can be

modified only once by a user. The user buys a blank PROM and enters the

desired contents using a PROM program. Inside the PROM chip,there are

smallfuses which are burnt open during programming. It can be programmed

only once and is not erasable.

 Erasable Programmable Read-Only Memory(EPROM): This is programmed

44 Computer Hardware and Architecture

with the use of very high voltages and exposure to approximately 20 minutes of

intense ultraviolet (UV) light

 Electrically-Erasable Programmable Read-Only Memory (EEPROM): This is

used in many older computer BIOS chips, is non-volatile storage that can be

erased and programmed several times and allows only one location at a time to

be written or erased. An updated version of EEPROM is flash memory; this

allows numerous memory locations to be altered simultaneously.

 Ultraviolet-Erasable Programmable Read-Only Memory (UV-EPROM): This is

read-only memory that can be erased by the use of ultraviolet light and then

reprogrammed.

Cache Memory

Cache memory is a small-sized type of volatile computer memory that provides high-

speed data access to a processor and stores frequently used computer programs,

applications and data. It is the fastest memory in a computer, and is typically integrated

onto the motherboard and directly embedded in the processor or main random access

memory (RAM).

Three types of Cache memory

 Level 1 Cache ( L1Cache)

 Level 2 Cache ( L2 Cache)

 Level 3 Cache(L3 Cache)

L1 Cache

A level 1 cache (L1 cache) is a memory cache that is directly built into the

microprocessor, which is used for storing the microprocessor’s recently accessed

information, thus it is also called the primary cache. It is also referred to as the internal

cache or system cache.L1 cache is the fastest cache memory, since it is already built

within the chip with a zero wait-state interface, making it the most expensive cache

Computer Hardware and Architecture 45

among the CPU caches. However, it has limited size. It is used to store data that was

accessed by the processor recently, critical files that need to be executed immediately

and it is the first cache to be accessed and processed when the processor itself performs

a computer instruction.

L2 Cache

A level 2 cache (L2 cache) is a CPU cache memory that is located outside and separate

from the microprocessor chip core, although, it is found on the same processor chip

package. Earlier L2 cache designs placed them on the motherboard which made them

quite slow.

Including L2 caches in microprocessor designs are very common in modern CPUs

even though they may not be as fast as the L1 cache, but since it is outside of the core,

the capacity can be increased, and it is still faster than the main memory. A level 2

cache is also called the secondary cache or an external cache

L3 Cache

A Level 3 (L3) cache is a specialized cache that that is used by the CPU and is usually

built onto the motherboard and, in certain special processors, within the CPU module

itself. It works together with the L1 and L2 cache to improve computer performance

by preventing bottlenecks due to the fetch and execute cycle taking too long. The L3

cache feeds information to the L2 cache, which then forwards information to the L1

cache. Typically, its memory performance is slower compared to L2 cache, but is still

faster than the main memory (RAM).

Virtual Memory

Virtual memory is the separation of logical memory from physical memory. This

separation provides large virtual memory for programmers when only small physical

memory is available.Virtual memory is used to give programmers the illusion that they

have a very large memory even though the computer has a small main memory. It

makes the task of programming easier because the programmer no longer needs to

worry about the amount of physical memory available.

46 Computer Hardware and Architecture

The operating system, such as Microsoft Windows or Apple's OS X, creates a set of

virtual addresses for each program. The OS translates virtual addresses into physical

ones, dynamically fitting programs into RAM as it becomes available.

2.2.2 Secondary Memory

This memory is permanent in nature. It is used to store the different programs and the

information permanently (which were temporarily stored in RAM). It holds the

information till we erase it.

Different types of secondary storage devices are:

Hard Disc, Compact Disc, DVD, Pen Drive, Flash Drive, etc.

Hard Disc

This is the main storage device of the computer which is fixed inside the CPU box. Its

storage capacity is very high that varies from 200 GB to 3 TB. As it is fixed inside the

CPU box, it is not easy to move the hard disc from one computer to another.

Computer Hardware and Architecture 47

A hard disc contains a number of metallic discs which are called platters. Information

is recorded on the surface of the platters in a series of concentric circles. These circles

are called Tracks. For the purpose of addressing information, the surface is considered

to be divided into segments called Sectors. This division helps in the proper

organization of data on the platter and helps in maximum utilization of the storage

space.

Memory Measurement Unit

Memory unit is the amount of data that can be stored in the storage unit. This storage

capacity is expressed in terms of Bytes.The following table explains the main memory

storage units –

S.No. Unit & Description

1 Bit (Binary Digit)

A binary digit is logical 0 and 1 representing a passive or an active state

of a component in an electric circuit.

2 Nibble

A group of 4 bits is called nibble.

3 Byte

A group of 8 bits is called byte. A byte is the smallest unit,

which can represent a data item or a character.

4 Word

48 Computer Hardware and Architecture

A computer word, like a byte, is a group of fixed number of bits

processed as a unit, which varies from computer to computer

but is fixed for each computer.

The length of a computer word is called word-size or word

length. It may be as small as 8 bits or may be as long as 96 bits.

A computer stores the information in the form of computer

words.

The following table lists some higher storage units –

S.No. Unit & Description

1 Kilobyte (KB)

1 KB = 1024 Bytes

2 Megabyte (MB)

1 MB = 1024 KB

3 GigaByte (GB)

1 GB = 1024 MB

4 TeraByte (TB)

1 TB = 1024 GB

5 PetaByte (PB)

1 PB = 1024 TB

2.3 Memory addressing

The bus determines a fixed number of CPU memory addresses assigned according to

CPU requirements. The CPU then processes physical memory in individual

segments.The operating system's read-only memory (ROM) basic input/output system

Computer Hardware and Architecture 49

(BIOS) programs and device drivers require memory addresses. Before processing,

input device/keyboard data, stored software or secondary storage must be copied to

RAM with assigned memory addresses.Memory addresses are usually allocated during

the boot process. This initiates the startup BIOS on the ROM BIOS chip, which

becomes the assigned address. To enable immediate video capability, the first memory

addresses are assigned to video ROM and RAM, followed by the following assigned

memory addresses:

 Expansion card ROM and RAM chips

 Motherboard dual inline memory modules, single inline memory modules or

Rambus inline memory modules

 Other devices

Retrieve from https://www.techopedia.com/definition/323/memory-address

2.5 Error-correcting code

Error-correcting code (ECC) memory is a type of computer data storage specifically

designed to detect, correct and monitor most common kinds of interior data corruption.

As data is processed, ECC memory equipped with a special algorithm constantly scans

and corrects single-bit memory errors. This ensures that no erroneous or corrupt data

is accidentally stored in memory. It is typically found and used in systems with high-

value data such as scientific and financial computing systems.

Traditional ECC memory uses Hamming codes, while others use triple modular

redundancy, which is preferred due to having faster hardware in comparison to

Hamming error correction hardware. Earlier implementations of ECC memory mask

correctable errors, acting as if the error never occurred, and only report non-correctable

errors. Recent implementations record both correctable errors and non-correctable

errors.ECC memory utilizes parity bits in storing encrypted code. In parallel to data

being written to memory, its ECC code is stored. Once data is read, the stored ECC

code is compared to the ECC code generated when the data was read. If in any case

there is a mismatch, it is decrypted by the parity bits to determine which bit has an

error and is immediately corrected.

50 Computer Hardware and Architecture

ECC memory utilizes parity bits in storing encrypted code. In parallel to data being

written to memory, its ECC code is stored. Once data is read, the stored ECC code is

compared to the ECC code generated when the data was read. If in any case there is a

mismatch, it is decrypted by the parity bits to determine which bit has an error and is

immediately corrected.

2.6 Memory Package

Memory package is a small circuit board that contains memory chips.

SIMM,DIMM,SODIMM, AND RIMM are some of the memory packages. These

packages are the form factors of RAM chip. The installation of a memory depends on

the form factors of a RAM. A form factor is the size and shape of the memory

packages.

Computer Hardware and Architecture 51

Single In-line Memory Module ( SIMM)

SIMM is a small circuit board designed to hold memory chips. It contains pins for

accepting data from the control circuit. These circuit boards or modules are known as

packages. There are various SIMM packages available based on the number of pins it

contains. For example, there are 30 pin packages and 72 pin packages.

The capacities of a 30-pin package SIMM package are 256 Kb, 1 MB, 2 MB,

4MB,8MB,16MB RAM. It contains 2,4,0r 8 chips per module. A 30-pin SIMM

package has a data bus width of 9 bits with 9- bit parity. Parity checks the accuracy of

the data transmission. An odd parity and an even parity are the two modes of parity

checking.

A 72-pin SIMM package has 32-bit data width with 36-bit parity. PS/2 is another term

used for the 72-pin package. The capacities of a 72- pin packages are 1 MB, 2MB,

4MB,8MB,16MB,32MB,64, MB, AND 128MB RAM. It contains 2,4,8, or 16 data

chips per module. FPM DRAM uses a 72-pin package.

Dual In-line Memory Module (DIMM)

DIMM package is also a small circuit board that contains the memory chips. The

difference between the SIMM and DIMM is that DIMM is a 168-pin package. The

data of the DIMM packages are 64-bit ,72-bit, or 80-bit. A 168-pin DIMM package is

available in thr SDRAM, EDO or FPM DRAM chips.

Small outline Dual In-Line Memory Module (SODIMM)

Laptops and notebook systems uses this package. It is the smallest version of the

DIMM. The SODIMM package has a notch at the bottom of the circuit board. This

notch helps in inserting the SODIMM package is the memory socket. SODIMM

packages are available with 144 and 200 pins. A 144- pin SODIMM package has 64-

bit data path. The FPM DRAM and EDO RAM use this package. The 72 pins on both

the sides of the

package divide a 144-pin package

A 200-pin SODIMM package has 64-bit data path. PC2 100 memory and pc2700

memory use this package. The 100 pins on both sides of the package divide a 200-Pin

package .

52 Computer Hardware and Architecture

Micro DIMM

Micro DIMM stands for Micro Dual Inline Memory Module. This package is smaller

than DIMM and SODIMM packages. The sub-notebook systems use these memory

packages. The Micro DIMM package pins connect the memory module with the

memory socket. These pins provide two communication lines for the module and the

system. This Package does not have the notch at the bottom. Micro DIMM packages

are available with 144 and 172 pins.

Rambus Inline Memory Module (RIMM)

RDRAM chip uses the RIMM memory package . This package is same as the DIMM

package. It only differs in the pin configuration. The high bandwidth and the low

latency application use this memory package.The RIMM package has a data storage

speed of 600 MHz, 711 MHz, 800 MHz and 1066 MHz. It has 184 connecting pins.

The distance between each pn in the RIMM package is 1mm. This package starts

operating from 2.5 voltage supply. The RIMM package are available in 16-bit data

buses 32-bit data buses, and 64-bit data buses. The memory bandwidth of the RIMM

package is up to 9.6 GB per second

References:

https://www.studytonight.com/computer-architecture/mapping-and-virtual-memory

https://www.tutorialspoint.com/computer_fundamentals/computer_memory_units.ht

https://www.techopedia.com/definition/323/memory-address

Computer Hardware and Architecture 53

UNIT - 3

Processor

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

3.1 Hardwired and Micro programmed

To execute an instruction, the control unit of the CPU must generate the required

control signal in the proper sequence. There are two approaches used for generating

the control signals in proper sequence as Hardwired Control unit and Micro-

programmed control unit.

Hardwired Control Unit

The control hardware can be viewed as a state machine that changes from one state to

another in every clock cycle, depending on the contents of the instruction register, the

condition codes and the external inputs. The outputs of the state machine are the

control signals. The sequence of the operation carried out by this machine is

determined by the wiring of the logic elements and hence named as “hardwired”.

 Fixed logic circuits that correspond directly to the Boolean expressions are used

to generate the control signals.

 Hardwired control is faster than micro-programmed control.

 A controller that uses this approach can operate at high speed.

 RISC architecture is based on hardwired control unit

54 Computer Hardware and Architecture

Micro-programmed Control Unit

 The control signals associated with operations are stored in special memory units

inaccessible by the programmer as Control Words.

 Control signals are generated by a program are similar to machine language

programs.

 Micro-programmed control unit is slower in speed because of the time it takes

to fetch microinstructions from the control memory.

Some Important Terms

1. Control Word: A control word is a word whose individual bits represent various

control signals.

2. Micro-routine: A sequence of control words corresponding to the control

sequence of a machine instruction constitutes the micro-routine for that

instruction.

3. Micro-instruction: Individual control words in this micro-routine are referred to

as microinstructions.

4. Micro-program: A sequence of micro-instructions is called a micro-program,

which is stored in a ROM or RAM called a Control Memory (CM).

5. Control Store: the micro-routines for all instructions in the instruction set of a

Computer Hardware and Architecture 55

computer are stored in a special memory called the Control Store.

Types of Micro-programmed Control Unit: Based on the type of Control Word

stored in the Control Memory (CM), it is classified into two types.

1. Horizontal Micro-programmed control Unit : The control signals are

represented in the decoded binary format that is 1 bit/CS. Example: If 53 Control

signals are present in the processor than 53 bits are required. More than 1 control

signal can be enabled at a time.

 It supports longer control word.

 It is used in parallel processing applications.

 It allows higher degree of parallelism. If degree is n, n CS are enabled at a time.

 It requires no additional hardware(decoders). It means it is faster than Vertical

Microprogrammed.

 It is more flexible than vertical microprogrammed

2. Vertical Micro-programmed control Unit : The control signals re represented

in the encoded binary format. For N control signals- Log2(N) bits are required.

 It supports shorter control words.

 It supports easy implementation of new conrol signals therefore it is more

flexible.

56 Computer Hardware and Architecture

 It allows low degree of parallelism i.e., degree of parallelism is either 0 or 1.

 Requires an additional hardware (decoders) to generate control signals, it implies

it is slower than horizontal microprogrammed.

 It is less flexible than horizontal but more flexible than that of hardwired control

unit.

GATE CS Corner Questions

Practicing the following questions will help you test your knowledge. All questions

have been asked in GATE in previous years or in GATE Mock Tests. It is highly

recommended that you practice them.

1. GATE CS 2004, Question 66

2. GATE CS 2002, Question 32

3.2 ArithmeticLogic Unit

Inside a computer, there is an Arithmetic Logic Unit (ALU), which is capable of

performing logical operations (e.g. AND, OR, Ex-OR, Invert etc.) in addition to the

arithmetic operations (e.g. Addition, Subtraction etc.). The control unit supplies the

data required by the ALU from memory, or from input devices, and directs the ALU

to perform a specific operation based on the instruction fetched from the memory.

ALU is the “calculator” portion of the computer.

An arithmetic logic unit(ALU) is a major component of the central processing unit of

Computer Hardware and Architecture 57

the a computer system. It does all processes related to arithmetic and logic operations

that need to be done on instruction words. In some microprocessor architectures, the

ALU is divided into the arithmetic unit (AU) and the logic unit (LU).

An ALU can be designed by engineers to calculate many different operations. When

the operations become more and more complex, then the ALU will also become more

and more expensive and also takes up more space in the CPU and dissipates more heat.

That is why engineers make the ALU powerful enough to ensure that the CPU is also

powerful and fast, but not so complex as to become prohibitive in terms of cost and

other disadvantages.

ALU is also known as an Integer Unit (IU). The arithmetic logic unit is that part of the

CPU that handles all the calculations the CPU may need. Most of these operations are

logical in nature. Depending on how the ALU is designed, it can make the CPU more

powerful, but it also consumes more energy and creates more heat. Therefore, there

must be a balance between how powerful and complex the ALU is and how expensive

the whole unit becomes. This is why faster CPUs are more expensive, consume more

power and dissipate more heat.

Different operation as carried out by ALU can be categorized as follows –

 logical operations: These include operations like AND, OR, NOT, XOR, NOR,

NAND, etc.

 Bit-Shifting Operations: This pertains to shifting the positions of the bits by a

certain number of places either towards the right or left, which is considered a

multiplication or division operations.

 Arithmetic operations: This refers to bit addition and subtraction. Although

multiplication and division are sometimes used, these operations are more

expensive to make. Multiplication and subtraction can also be done by repetitive

additions and subtractions respectively.

3.3 Types of Register

Computer or microcontrollers need memory to store data & programs that it needs to

process later. These memory devices may be hard drives, memory sticks but the CPU

itself need some storage space to store the necessary commands & instruction for data

58 Computer Hardware and Architecture

processing. That is where registers come in.

A register is the smallest storage units built inside the processor for quick store &

transfer of data & instruction necessary for the processor. The CPU can directly access

the register for quick actions. They store operands or instruction that is currently being

used by the processor.There are different types of Register each having a special

purpose

 Data Register Or DR

As its name suggests, data register temporarily store the data or operand that is

currently being processed by the processor.

 Accumulator Register or AR

This register is used to accumulate the operands used by the ALU (Athematic Logic

Unit) during any athematic or logical processing. It stores the initial operands,

intermediate and final result before sending to relevant register block.

 Program Counter or PC

Computer Hardware and Architecture 59

This is a special register. This register stores the address of the next address to be

fetched for execution. During each machine cycle, it increments, pointing towards the

address of the next instruction to be fetched.

 Instruction Register or IR

This register holds the instruction commands from other memory units. It stores the

instructions ready to be fetched by the control unit for processing.

 Memory Address Register or MAR

This register stores the address location of the memory where the CPU wants to read

or write some data.

 Memory Buffer Register or MBR

This is a buffer register for any data or instruction going from or to any memory. It

holds the instruction/data before sending it to IR/ AR respectively.

 Stack Control Register or SCR

The name suggests a stack (set) of the memory block that stores that data using FILO

(First in last out).

 Flag Register or FR

The flag means alarm or special condition, this type of special register indicates the

flags occurred during any operation of the processor. There are different types of flags

such as interrupt flag, Data overflow flag, zero flag, parity flag etc. all controlled by

flag register using each bit of the register.

 I/O Address Register or I/O AR

This type of register stores the address of any input/output module or system connected

with the processor.

 I/O Buffer Register or I/O BR

This Register holds the data that is to be transferred between the I/O module and the

CPU.

3.4 Bus Architecture

Bus is a group of conducting wires which carries information, all the peripherals are

connected to microprocessor through Bus.Diagram to represent bus organization

60 Computer Hardware and Architecture

system of 8085 Microprocessor.

Functions of Buses in Computers

Summary of functions of buses in computers

1. Data sharing: All types of buses found in a computer transfer data between the

computer peripherals connected to it.The buses transfer or send data either in the

serial or parallel method of data transfer. This allows for the exchange of 1, 2, 4

or even 8 bytes of data at a time. (A byte is a group of 8 bits). Buses are classified

depending on how many bits they can move at the same time, which means that

we have 8-bit, 16-bit, 32-bit or even 64-bit buses.

2. Addressing: A bus has address lines, which match those of the processor. This

allows data to be sent to or from specific memory locations.

3. Power: A bus supplies power to various peripherals connected to it.

4. Timing: The bus provides a system clock signal to synchronize the peripherals

attached to it with the rest of the system. The expansion bus facilitates easy

connection of more or additional components and devices on a computer such as

a TV card or sound card.

There are three types of buses.

Address bus

It is a group of conducting wires which carries address only. Address bus is

unidirectional because data flow in one direction, from microprocessor to memory or

from microprocessor to Input/output devices (That is, Out of Microprocessor).Length

of Address Bus of 8085 microprocessor is 16 Bit (That is, Four Hexadecimal Digits),

ranging from 0000 H to FFFF H, (H denotes Hexadecimal). The microprocessor 8085

Computer Hardware and Architecture 61

can transfer maximum 16 bit address which means it can address 65, 536 different

memory location.

The Length of the address bus determines the amount of memory a system can address.

Such as a system with a 32-bit address bus can address 2^32 memory locations. If each

memory location holds one byte, the addressable memory space is 4 GB.However, the

actual amount of memory that can be accessed is usually much less than this theoretical

limit due to chipset and motherboard limitations.

Data bus

It is a group of conducting wires which carries Data only.Data bus is bidirectional

because data flow in both directions, from microprocessor to memory or Input/Output

devices and from memory or Input/Output devices to microprocessor. Length of Data

Bus of 8085 microprocessor is 8 Bit (That is, two Hexadecimal Digits), ranging from

00 H to FF H. (H denotes Hexadecimal).When it is write operation, the processor will

put the data (to be written) on the data bus, when it is read operation, the memory

controller will get the data from specific memory block and put it into the data bus.

The width of the data bus is directly related to the largest number that the bus can

carry, such as an 8 bit bus can represent 2 to the power of 8 unique values, this equates

to the number 0 to 255.A 16 bit bus can carry 0 to 65535.

Control bus

It is a group of conducting wires, which is used to generate timing and control signals

to control all the associated peripherals, microprocessor uses control bus to process

data, that is what to do with selected memory location. Some control signals are:

 Memory read

 Memory write

 I/O read

 I/O Write

 Opcode fetch

If one line of control bus may be the read/write line. If the wire is low (no electricity

flowing) then the memory is read, if the wire is high (electricity is flowing) then the

62 Computer Hardware and Architecture

memory is written.

3.5 Instruction Execution

Memory consists of a large array of words or bytes, each with its own address. The

CPU fetches instructions from memory according to the value of the program counter.

These instructions may cause additional loading from and storing to specific memory

addresses. A typical instruction-execution cycle, for example, first fetches an

instruction from memory The instruction is then decoded and may cause operands to

be fetched from memory.

After the instruction has been executed on the operands, results may be stored back in

memory. The memory unit see shortly a stream of memory addresses; it does not know

how they are generated (by the instruction counter, indexing, indirection, literal

addresses, and so on) or what they are for (instructions or data). Accordingly, we can

ignore a program generates a memory address. We are interested only in the sequence

of memory addresses generated by the running program.

The following is a summary of the six steps used to execute a single instruction.

Step 1: Fetch instruction.

Step 2: Decode instruction and Fetch Operands.

Step 3: Perform ALU operation.

Step 4: Access memory.

Step 5: Write back result to register file.

Step 6: Update the PC.

The Instruction Cycle

Each phase of Instruction Cycle can be decomposed into a sequence of elementary

Computer Hardware and Architecture 63

micro-operations. In the above examples, there is one sequence each for the Fetch,

Indirect, Execute and Interrupt Cycles.

The Indirect Cycle is always followed by the Execute Cycle. The Interrupt Cycle is

always followed by the Fetch Cycle. For both fetch and execute cycles, the next cycle

depends on the state of the system.

64 Computer Hardware and Architecture

We assumed a new 2-bit register called Instruction Cycle Code (ICC). The ICC

designates the state of processor in terms of which portion of the cycle it is in:-

00 : Fetch Cycle

01 : Indirect Cycle

10 : Execute Cycle

11 : Interrupt Cycle

At the end of the each cycles, the ICC is set appropriately.The above flowchart

of Instruction Cycle describes the complete sequence of micro-operations, depending

only on the instruction sequence and the interrupt pattern(this is a simplified example).

The operation of the processor is described as the performance of a sequence of micro-

operation.

Different Instruction Cycles

The Fetch Cycle

At the beginning of the fetch cycle, the address of the next instruction to be executed

is in the Program Counter(PC).

Step 1: The address in the program counter is moved to the memory address register

(MAR), as this is the only register which is connected to address lines of the system

bus.

Computer Hardware and Architecture 65

Step 2: The address in MAR is placed on the address bus, now the control unit issues

a READ command on the control bus, and the result appears on the data bus and is

then copied into the memory buffer register (MBR). Program counter is incremented

by one, to get ready for the next instruction. (These two action can be performed

simultaneously to save time)

Step 3: The content of the MBR is moved to the instruction register(IR).

Thus, a simple Fetch Cycle consist of three steps and four micro-operation.

Symbolically, we can write these sequence of events as follows:-

Here ‘I’ is the instruction length. The notations (t1, t2, t3) represents successive time

units. We assume that a clock is available for timing purposes and it emits regularly

spaced clock pulses. Each clock pulse defines a time unit. Thus, all time units are of

equal duration. Each micro-operation can be performed within the time of a single time

unit.First time unit: Move the contents of the PC to MAR. Second time unit: Move

contents of memory location specified by MAR to MBR. Increment content of PC by

I. Third time unit: Move contents of MBR to IR.

66 Computer Hardware and Architecture

Note: Second and third micro-operations both take place during the second time unit.

The Indirect Cycles

Once an instruction is fetched, the next step is to fetch source operands. Source

Operand is being fetched by indirect addressing( it can be fetched by any addressing

mode, here its done by indirect addressing). Register-based operands need not be

fetched. Once the opcode is executed, a similar process may be needed to store the

result in main memory. Following micro-operations takes place:-

Step 1: The address field of the instruction is transferred to the MAR. This is used to

fetch the address of the operand.

Step 2: The address field of the IR is updated from the MBR.(So that it now contains

a direct addressing rather than indirect addressing)

Step 3: The IR is now in the state, as if indirect addressing has not been occurred.

Note: Now IR is ready for the execute cycle, but it skips that cycle for a moment to

consider the Interrupt Cycle .

The Execute Cycle

The other three cycles(Fetch, Indirect and Interrupt) are simple and predictable. Each

of them requires simple, small and fixed sequence of micro-operation. In each case

same micro-operation are repeated each time around.

Execute Cycle is different from them. Like, for a machine with N different opcodes

there are N different sequence of micro-operations that can occur.

Lets take an hypothetical example :-

Consider an add instruction:

Computer Hardware and Architecture 67

Here, this instruction adds the content of location X to register R. Corresponding

micro-operation will be:-

We begin with the IR containing the ADD instruction.

Step1: The address portion of IR is loaded into the MAR.

Step2: The address field of the IR is updated from the MBR, so the reference memory

location is read.

Step 3: Now, the contents of R and MBR are added by the ALU.

Lets take a complex example :-

Here, the content of location X is incremented by 1. If the result is 0, the next

instruction will be skipped. Corresponding sequence of micro-operation will be :-

Here, the PC is incremented if (MBR) = 0. This test (is MBR equal to zero or not) and

action (PC is incremented by 1) can be implemented as one micro-operation.

Note : This test and action micro-operation can be performed during the same time

unit during which the updated value MBR is stored back to memory.

68 Computer Hardware and Architecture

The Interrupt Cycle

At the completion of the Execute Cycle, a test is made to determine whether any

enabled interrupt has occurred or not. If an enabled interrupt has occurred then

Interrupt Cycle occurs. The nature of this cycle varies greatly from one machine to

another.Lets take a sequence of micro-operation:-

Step 1: Contents of the PC is transferred to the MBR, so that they can be saved for

return.

Step 2: MAR is loaded with the address at which the contents of the PC are to be

saved.PC is loaded with the address of the start of the interrupt-processing routine.

Step 3: MBR, containing the old value of PC, is stored in memory.

Note: In step 2, two actions are implemented as one micro-operation. However, most

processor provide multiple types of interrupts, it may take one or more micro-operation

to obtain the save_address and the routine_address before they are transferred to the

MAR and PC respectively.

MEMORY ADDRESSING TEHNIQUES

General considerations concerning the memory addressing

It has been presented the fact that in modern computers the memory unit is

implemented with integrated modules. The connection between CPU and main

memory is realized by means of three buses:

 The address busADRBUS;

 The data bus DATABUS;

 The control bus CONTROLBUS.

Computer Hardware and Architecture 69

The address bus is unidirectional; the data bus is bidirectional, while the control bus

contains command and status lines. The memory is organized on locations:

k-1k

k+1

-1

A memory location has m ranks noted Bm-1, ... B1, B0.

Reading and writing the memory is performed in parallel, in other words one reads or

writes an m bit word at a time. Addressing the memory is done via the address bus

(ADRBUS) and it isassumed this bus comprises n lines. Each combination of bits of

this bus defines a certain address. The connection between the bus content and a

specific location is done via a decoding process. If the address bus has n lines then the

address set is2n.

A = {0,1,...2n

-1}

where: A = address space

On the other hand, given a certain memory geometry, it results the set of physical

locations where m bit words are stored.

Bm-1 ......... B1 B0

... ... ... ...

70 Computer Hardware and Architecture

Definition: The set of all physical locations defined by a geometry is called the space

of the memoryM.

Theconnectionbetweentheaddressspaceandthememoryspaceisgivenbyatranslation

function, defined as: fT : A €M.

In accordance to the previously mentioned notions, this function corresponds to a

decoding function. In case of simple systems (microcomputers) the two sets will be

identical M = A so f is a simplefunction.

When the width of the memory word is not enough to represent the data, then several

consecutive locations are used. If for instance, a datum is representable on two words

in memory – AIU, meaning addressable informational unit, then, in order to represent

it, the first location is used for the least significant word (from address j), and the next

location (address j+1) for the most significantword.

Modern processors present memory management facilities. These memory

management operations refer to virtual memory implementation, memory protection,

etc.The Memory Management Unit – MMU can be built in the control unit inside the

CPU or can be external (with respect to the same control unit). In particular, in case of

microprocessors it can be incorporated or sold separately as an additional module –

the MMU module.

In order to implement the concept of virtual memory the next simplified scheme is

used:

AL represents the logic address generated by the CPU when reading the current

instruction. After processing the logic address inside the MMU, it results the physical

address. In case the logic address has no physical correspondent in the main memory

then transfer commands (CT) are generated, for transfer between external(secondary)

memory and mainmemory.

The practical implementation of the virtual memory concept is based on the transfer

Computer Hardware and Architecture 71

of blocks of information between secondary and main memories. The most widespread

method is memory segmentation.

It has been already shown that each instruction at machine level comprises two main

fields:

OPCOD

ADDRES

n l

The address field comprises those constitutive elements of the logic address;

processing this logic address one finds the effective or physical address. In case of the

effective address:

AE = f(AL)

where:

AL – logic address; AE – effective address

Besides these constitutive elements in the address field forming the logic address, there

may exist other elements stored in CPU registers or memory.

In modern computers usually the effective and logic addresses are not the same. Quite

the opposite, this function is more and more complex. The purpose is to ensure greater

flexibility in programming, as well as shortening the length of the programs. It is also

envisaged shortening the instructions length, even if the total volume of addressed

memory (the memory space) is constantly increasing.

It has been shown that the instruction cycle comprises two main phases. Each of these

phases is divided in sub-phases as in the next figure:

72 Computer Hardware and Architecture

Fetch Execute

Fetch AE Fetch

Data

Execute

The second phase (AE) is important in the calculation of the operands effective

addresses (determination of AE).

I. Assumed operandaddressing

There exist situations in which the operand is assumed as known, based on the

OPCODE, so it doesn’t need to be explicitly emphasized in the instruction, neither as

value, nor as address.

For example:

 Increment instruction – the increment 1 is assumed as already known, and if this

instruction is executed then the value of the accumulator register is increased

with1.

 SHIFT instruction – one assumes the shift value is 1, there is no need for

supplementary specifications.

II. Implicitaddressing

It has been presented that in the case of instructions with one or two addresses there is

a special register in the CPU, the accumulator, which is used when performing the

operations. This isbecause of the way the computer itself is designed and built. It is not

necessary to specify it in any other way.

ACC

(ADR1)*

(ADR2)

ACC

(ADR)*(

ACC)

Moreover, in modern CPUs, one can designate certain general registers to store an

operand’s address. These general registers are generally referred to as DATA

COUNTER. When designing a CPU, the implicit addressing is considered in the

OPCODE ADR

OPCODE ADR1 ADR2

Computer Hardware and Architecture 73

following manner: the operand is read from memory from the address specified by the

Data Counter, this register acts as a counter with increment/decrement facilities. This

way, it allows addressing of a whole block of data. One may notice implicit addressing

through self-incrementation and implicit addressing through self- decrementation.

Additionally, a load operation must be implemented, in order to be able to load the

start address of the data block.

One can notice two variants in which the operand read operation is performed:

 Before incrementation/decrementation; incrementation/decrementationpost-

operation;

 After incrementation/decrementation; incrementation/decrementationpre-

operation.

Implicit addressing with post operation incrementation

This is an implicit addressing with post operation incrementation.

Step no 1 – the location A212 is addressed, and a CLEAR is performed

Step no 2 – the Data Counter is incremented, thus having the value A213.

74 Computer Hardware and Architecture

Implicit addressing with pre operation decrementation

This is an implicit addressing with pre operation decrementation.Step no 1 – the DC

content is modified/decremented, to the value BE23 Step no 2 – a CLEAR operation

is performed at the address BE23.

Remark: There are CPUs that can define simultaneously several DCs, therefore it is

possible to process several data blocks.

I. Immediate addressing

This addressing mechanism violates the general addressing principle; the operand is

not separately stored but is an integral part of the instruction. This type of operand is

called immediate data.

OPCODE ID OPERAND

Considering that there is the OPCODE field in the instruction format, it results that the

length of the operand is shorter than the standard operand length, but the main

advantage is that this data is immediately available after the fetch instruction phase,

the fetch data phase being no longer necessary. Each fetch implies a memory read, a

time consuming operation, but the execution is faster when the data is available

together with the instruction itself.

In case of minicomputers with 16 bit words, the immediate data that comes with the

OPCODE is a 16 bit word (first the OPCODE and then the data).

8 bits

.........

OPCODE Instruction

Immediate

data

.........

O. M.

Computer Hardware and Architecture 75

II. Direct addressing

The direct addressing represents the natural memory addressing mode: the logic

address coincides with the effective address.

One can notice the following direct addressing sub classes:

1. direct addressing to aregister;

2. direct addressing tomemory;

3. direct addressing to an input-outputdevice;

4. combined directaddressing.

1. Direct addressing to register

All modern processors contain a certain number of general registers with very fast

access, whose reunion forms the local memory. The current data to be processed is

brought into these registers. Because the number of these registers is limited (small),

the register address is also small (important advantage).

On the other hand the access to data is much faster, because the memory read cycle is

not started (because data isn’t read from main memory). Reading data from these local

registers / local memory is performed extremely fast, due to the fact that they are CPU

components.

16 bits

.........

OPCODE Instruction

Immediate

data

.........

O. M.

76 Computer Hardware and Architecture

Direct addressing to register

2. Direct addressing tomemory

In this case, the operand (data) is located in the main memory, in the data. Addressing

the main memory is done by means of MAR (memory address register). If the memory

has 2nlocations then the address field must be on n bits.

Because the modern memory modules are getting larger with each day, it results that

the number of ranks used for address is steadily increasing also, therefore the

instructions whose operands are in memory and are retrieved in this manner necessitate

a large number of bits (longer length).

Direct addressing to memory

Executing such an instruction assumes transfer of the logic address from the address

field into the MAR register, start of a memory read cycle and extraction of the operand

from the addressed location.

In case of the 8 bit microcomputers such an instruction has 3 bytes:

Computer Hardware and Architecture 77

 the first byte is theOPCODE;

 the second byte is the inferior half of theaddress;

 the third byte is the superior half of theaddress.

ROM

.........

OPCODE

INF ADR

SUP ADR

.........

After reading the first byte (OPCODE) the control unit decodes the instruction and

thus knows it is a 3 byte instruction with direct addressing tomemory.

3. Direct addressing to input-outputdevices

This category of instructions is very diverse and should contain the following fields:

OPCODE ID Channel address Peripheral device address

4. Combined addressing

There are situations when one operand is located in the memory and the second in a

general register so the instruction must contain both addresses. It is a combination of

the first two cases. If both operands would be in the memory the instruction would be

very long (a very inconvenient case).

II. Paged addressing

Paged addressing is a variant of the direct. It was created out of the need to shorten the

instruction length. It was shown that in case of addressing the memory the address

field is long (as the memory volume increases the address field is longer).

78 Computer Hardware and Architecture

There were searched solutions to shorten the address field. One efficient solution is

dividing the whole memory space in memory pages. This division is only conceptual

and simplifies memory addressing.

Each page has a fixed number of locations, and the number of pages depends on the

global volume of the memory and size of a page. The size of a page is linked to the

length of the address field in the instruction. If the address field has k bites then the

recommended size of a page is 2k

locations.

Example of memory organisation on pages

Paged organisation of the memory is used in virtual memory as well. The pages can

be located at fixed addresses in case of a fixed page or at mobile addresses in case of

a dynamic page.

Example: it is considered an instruction with an 8 bit address field; then a page will

contain 256 locations.

1. Direct addressing to pagezero

It is used the address field on 8 bits (in general k bits) of the instruction to address the

256 locations, but only in page zero. The selected location is read and the operand

transferred into the ALU.The advantage of addressing into the page zero is a small

length of the. Instead of using 16 bits for the address (in general n bits) one uses only

8 bits (in general k bits where n > k).

Computer Hardware and Architecture 79

Direct addressing to page zero

The main disadvantage is the access only to this page, with no possibility to access

another page.

2. Addressing the currentpage

In order to eliminate the disadvantages presented earlier, and to be able to address all

pages, a special mechanism will be used, combining a component of the instruction,

the logic address and a component from a CPU register, namely the PC. It is assumed

that the address has n bits for a total volume of addressable locations of 2n. Then the

memory is organised in pages of 2k locations, for a total of 2n-k pages. The least

significant part of the address formed of k bits allows addressing a location inside a

page and the most significant part of the address on n-k bits allows determination of

the right page. The n-k bits are taken from the most significant n-k bits of the program

counter. Combining the two parts is done through concatenation. The newly obtained

address is placed in the MAR which is on n bits and then the desired location is read

(a certain page, and a certainlocation).

80 Computer Hardware and Architecture

Addressing the current page

From the way the address is formed it results that the data required by an instruction

has to be located in the vicinity of that instruction. This vicinity is materialised by

conserving the samepage. So, when writing the program, and if using the same

addressing technique, the programmer will place the data in the same memory page,

because the page address is taken from the PC. When executing the current instruction,

the PC has a certain value, out of which the most significant (n-k) bits are taken to

form the address for the page containing theoperand.

There can result critical situations at the frontier between. It is known that after fetch

instruction it is issued the command to increment the PC. If for instance the current

instruction is located at the address 01FF (k=2, n - k = 2), then after incrementation

01FF + 1 = 0200 and the page address changes from 01 to 02.

(J+1)*2k

Computer Hardware and Architecture 81

3. Relative page addressing

The notion of current page presented above is replaced in this case with the notion of

relative page. This relative page is dynamic in the memory space. It is called relative

because it is centred on the current value of the PC. So, in this addressing technique

the PC is used with all its ranks. In the instruction the previously presented address

field (the logic address) is now called offset.

This offset represents the value with which the PC is added to find the operand. The

offset can be a positive binary number or a binary number with sign. The effective

address is the sum of the PC an the offset and the result is placed in MAR. If the offset

is positive then the base address of the relative page is the address contained in the PC

and the top is PC + Dmax, where Dmax is the maximum possible value of the offset. In

case the offset is a binary number with sign then the relative page is centred around

the location with the address given by the PC.

Page types

The PC has n ranks, while the offset has k ranks (k<n); the addition is performed on n

ranks.

82 Computer Hardware and Architecture

Relative page addressing

Example: It is considered an instruction already brought in the RI (instruction register)

having an OPCODE, an identifier and an offset = 2A, the address is written is

hexadecimal digits, PC = 1A00. It is performed a sum between the PC and the offset,

thus resulting the effective address.

VI. Base addressing

It resembles as mechanism the relative page addressing, except that instead of the PC,

it uses the content of another register or several registers called base registers; these

registers are part of the processor general registers group.

In this way it is eliminated the dependency between the data location and the program.

The base register has the same length as the MAR, and in the instruction, in the address

field it is placed the offset, which can be a positive binary number or a signed binary

number. The length of the offset is smaller than that of the MAR. The length of the

offset gives the width of the window, so a larger number of ranks in the address field

yields a larger window (a larger page).

Calculating the effective address is done by summing the content of the base register

Computer Hardware and Architecture 83

with theoffset. But because usually there are several base registers, a special field must

appear in the instruction, called field B, whose value points to the desired baseregister.

If for instance there are 8 base registers numbered 0 ... 7, then the B field must have

the width 3. In some computer architectures it is adopted the convention that if B = 0

then the effective address is given solely by the offset.

84 Computer Hardware and Architecture

Based addressing

Loading initial values in the base register and modifying them during the execution of

the program is done by means of software tools.

Definition: This addressing technique is called addressing through base and offset.

The content of the designated base register is either the center of the page containing

the data or the beginning of this page.

Because several base registers can be used it results that there can be simultaneously

defined several current pages for the data. When defining these pages special attention

must be paid to avoid addressoverlapping.

Indexed addressing

Indexed addressing is a variant of the based addressing. The base registers are replaced

with index registers. These registers are part of the processor general registers group.

The effective address is obtained in a similar manner as in based addressing: a

summing is performed between the contentof the index registers and the logic address

from theinstruction.

Definition. The content of the index register is called index.

What is particular to these index registers is the ability to perform a series of direct

Computer Hardware and Architecture 85

operations on them such as: increment, decrement, parallel load, addition, subtraction.

Theindexregistersarefrequentlyusedincomputerprogramming,especiallyindefiningcyc

les.One can simultaneously define several indexes, allowing thus declaration of several

cycles and thus nested cycles arepossible.

In the X field it is introduced the address of the index register. If there are s ranks then

there can be 2s

index registers. In the ID field (identification) there appear

combinations specifying a certain addressing technique.

Indexed addressing

Example of indexed addressing usage: it is required the transfer of a data block with

K components from the address area M1 ... Mk to R1...Rk. Usually, there should be

86 Computer Hardware and Architecture

written k transfer instructions like MOV. Programming is simplified if indexed

addressing is used.In the instructions in the address field the constants R1 and M1

appear, and one can perform increment operations on the index register. In the Rx index

the value of the index becomes zero then the data block transfer is complete.

Indirect addressing

Indirect addressing is a modern addressing technique that allows shortening the

programmed length and introduces flexibility in writing complex programmed.In

indirect addressing the logic address doesn’t lead us to the effective address of the

operand but to the address of a new instruction. The memory location pointed by the

address will be read and the data obtained will be interpreted as a new instruction.

Indirect addressing

In case of the microcomputers the indirect addressing is frequently performed as

implicit addressing by means of general registers of the CPU. In case of INTEL I8080

the register pair HL, each on 8 bits, is used as logic address for accessing the operative

(main) memory from where the operand is extracted. For instance there is the

instruction ADD M (which performs an addition between ACC and the content of the

memory location whose address is specified implicitly by the register pair HL content.

ACC €(ACC) + Mem ((H)(L))

Computer Hardware and Architecture 87

Addressing for a block of data

It has been shown that a computer may operate with variable length fields al well (data

blocks). To address them several options arepossible:

1. It is given the start and end addresses for theblock;

2. It is given the start address and the length of thefield;

3. It is given the start address and it is used a block delimiter meaning a

particularcombination of bits used only for identifying the block end. This is not

recommended as part of the memory is used to store thedelimiter.

II. Combined addressing techniques

Most of the microcomputers and computers use various combinations of the previously

presented addressing techniques, in order to take advantage of their benefits.

1. Multilevel indirect addressing. The indirect addressing is performed in several

cycles; each time the information extracted from memory is not an operand but

another instruction, except for the last read cycle. Usually there is a limit of

levels. For instance in case of the FELIX C family of computers the maximum

number of levels is5.

2. Indirect and indexed addressing.In accordance with its name, this technique

combines the two already presented techniques. The problem is when to perform

the indexing. There are 2 cases: indirect with post-indexing and with pre-

indexing. In the first situation, the indirect addressing is performed (it can be a

multilevel indirect addressing) and at the end it is added the value of the index

(from the index register specified in the instruction) thus resulting the effective

address. In the second situation it is performed the indexed addressing

mechanism at first, adding the logic address to the content of the index register

resulting the address where the pointer is located. The pointer is extracted, a new

addressing is performed and the operand is finallyread.

3. Based and indexed addressing. The effective address calculation mechanism is

thefollowing:

88 Computer Hardware and Architecture

Based Indexed Plus Displacement Addressing Mode

These addressing modes are a slight modification of the base/indexed addressing

modes with the addition of an eight bit or sixteen bit constant. The following are some

examples of these addressing modes:

mov al, disp[bx][si]

mov al, disp[bx+di]

mov al, [bp+si+disp]

mov al, [bp][di][disp]

You may substitute di in the figure above to produce the [bx+di+disp]

addressing mode.

Computer Hardware and Architecture 89

You may substitute di in the figure above to produce the [bp+di+disp]

addressing mode. Suppose bp contains 1000h, bx contains 2000h, si contains

120h, and di contains 5. Then mov al,10h[bx+si] loads al from

address DS:2130; mov ch,125h[bp+di] loads ch from location SS:112A;

and mov bx,cs:2[bx][di] loads bx from location CS:2007.

MASM Syntax for 8086 Memory Addressing Modes Microsoft's assembler uses

several different variations to denote indexed, based/indexed, and displacement lus

based/indexed addressing modes. You will see all of these forms used interchangeably

throughout this text. The following list some of the possible combinations that are legal

for the various 80x86 addressing modes:

disp[bx], [bx][disp], [bx+disp], [disp][bx], and [disp+bx]

[bx][si], [bx+si], [si][bx], and [si+bx]

disp[bx][si], disp[bx+si], [disp+bx+si], [disp+bx][si], disp[si][bx], [disp+si][bx],

[disp+si+bx], [si+disp+bx], [bx+disp+si], etc.

MASM treats the "[ ]" symbols just like the "+" operator. This operator is

commutative, just like the "+" operator. Of course, this discussion applies to all the

8086 addressing modes, not just those involving BX and SI. You may substitute any

legal registers in the addressing modes above.

References:

https://www.geeksforgeeks.org/different-instruction-cycles/

90 Computer Hardware and Architecture

Unit 4

Storage Devices

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

4.1 Memory Hierarchies

The memory in a computer can be divided into five hierarchies based on the speed as

well as use. The processor can move from one level to another based on its

requirements. The five hierarchies in the memory are registers, cache, main memory,

magnetic discs, and magnetic tapes. The first three hierarchies are volatile memories

which mean when there is no power, and then automatically they lose their stored data.

Whereas the last two hierarchies are not volatile which means they store the data

permanently. A memory element is the set of storage devices which stores the binary

data in the type of bits. In general, the storage of memory can be classified into two

categories such as volatile as well as non- volatile.

 Volatile Memory: This loses its data, when power is switched off.

 Non-Volatile Memory: This is a permanent storage and does not lose any data

when power is switched off.

 The total memory capacity of a computer can be visualized by hierarchy of

components. The memory hierarchy system consists of all storage devices

contained in a computer system from the slow Auxiliary Memory to fast Main

Computer Hardware and Architecture 91

Memory and to smaller Cache memory.

 Auxiliary memory access time is generally 1000 times that of the main memory,

hence it is at the bottom of the hierarchy.

 The main memory occupies the central position because it is equipped to

communicate directly with the CPU and with auxiliary memory devices through

Input/output processor (I/O).

 When the program not residing in main memory is needed by the CPU, they are

brought in from auxiliary memory. Programs not currently needed in main

memory are transferred into auxiliary memory to provide space in main memory

for other programs that are currently in use.

 The cache memory is used to store program data which is currently being

executed in the CPU. Approximate access time ratio between cache memory and

main memory is about 1 to 7~10

Memory Access Methods

Each memory type, is a collection of numerous memory locations. To access data from

any memory, first it must be located and then the data is read from the memory

location. Following are the methods to access information from memory locations:

1. Random Access: Main memories are random access memories, in which each

memory location has a unique address. Using this unique address any memory

location can be reached in the same amount of time in any order.

2. Sequential Access: This methods allows memory access in a sequence or in

order.

3. Direct Access: In this mode, information is stored in tracks, with each track

92 Computer Hardware and Architecture

having a separate read/write head.

Characteristics of Memory Hierarchy

The memory hierarchy characteristics mainly include the following.

Performance

Previously, the designing of a computer system was done without memory hierarchy,

and the speed gap among the main memory as well as the CPU registers enhances

because of the huge disparity in access time, which will cause the lower performance

of the system. So, the enhancement was mandatory. The enhancement of this was

designed in the memory hierarchy model due to the system’s performance increase.

Ability

The ability of the memory hierarchy is the total amount of data the memory can store.

Because whenever we shift from top to bottom inside the memory hierarchy, then the

capacity will increase.

Access Time

The access time in the memory hierarchy is the interval of the time among the data

availability as well as request to read or write. Because whenever we shift from top to

bottom inside the memory hierarchy, then the access time will increase

Cost per bit

When we shift from bottom to top inside the memory hierarchy, then the cost for each

bit will increase which means an internal Memory is expensive compared with external

memory.

Memory Hierarchy Design

The memory hierarchy in computers mainly includes the following.

Registers

Usually, the register is a static RAM or SRAM in the processor of the computer which

is used for holding the data word which is typically 64 or 128 bits. The program

counter register is the most important as well as found in all the processors. Most of

the processors use a status word register as well as an accumulator. A status word

Computer Hardware and Architecture 93

mathematical operation. Usually, computers like complex instruction set

computers have so many registers for accepting main memory, and RISC- reduced

instruction set computers have more registers.

Cache Memory

Cache memory can also be found in the processor, however rarely it may be another IC

(integrated circuit) which is separated into levels. The cache holds the chunk of data

which are frequently used from main memory. When the processor has a single core

then it will have two (or) more cache levels rarely. Present multi-core processors will

be having three, 2-levels for each one core, and one level is shared.

Main Memory

The memory unit that communicates directly within the CPU, Auxillary memory and

Cache memory, is called main memory. It is the central storage unit of the computer

system. It is a large and fast memory used to store data during computer operations.

Main memory is made up of RAM and ROM, with RAM integrated circuit chips

holing the major share.

 RAM: Random Access Memory

 DRAM: Dynamic RAM, is made of capacitors and transistors, and must be

refreshed every 10~100 ms. It is slower and cheaper than SRAM.

 SRAM: Static RAM, has a six transistor circuit in each cell and retains data, until

powered off.

 NVRAM: Non-Volatile RAM, retains its data, even when turned off. Example:

Flash memory.

 ROM: Read Only Memory, is non-volatile and is more like a permanent storage

for information. It also stores the bootstrap loader program, to load and start the

operating system when computer is turned on. PROM(Programmable

ROM), EPROM(Erasable PROM) and EEPROM(Electrically Erasable PROM)

are some commonly used ROMs.

Magnetic Disks

The magnetic disks in the computer are circular plates fabricated of plastic otherwise

94 Computer Hardware and Architecture

metal by magnetized material. Frequently, two faces of the disk are utilized as well as

many disks may be stacked on one spindle by read or write heads obtainable on every

plane. All the disks in computer turn jointly at high speed. The tracks in the computer

are nothing but bits which are stored within the magnetized plane in spots next to

concentric circles. These are usually separated into sections which are named as

sectors.

Magnetic Tape

This tape is a normal magnetic recording which is designed with a slender

magnetizable covering on an extended, plastic film of the thin strip. This is mainly

used to back up huge data. Whenever the computer requires to access a strip, first it

will mount to access the data. Once the data is allowed, then it will be unmounted. The

access time of memory will be slower within magnetic strip as well as it will take a

few minutes for accessing a strip.

Advantages of Memory Hierarchy

The need for a memory hierarchy includes the following.

 Memory distributing is simple and economical

 Removes external destruction

 Data can be spread all over

 Permits demand paging & pre-paging

 Swapping will be more proficient

Thus, this is all about memory hierarchy. From the above information, finally, we

can conclude that it is mainly used to decrease the bit cost, access frequency, and to

increase the capacity, access time. So it is up to the designer how much they need these

characteristics for satisfying the necessities of their consumers. Here is a question for

you, memory hierarchy in OS?

Computer Hardware and Architecture 95

UNIT - 5

Input/Output Organization

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

Content Elaboration

1. Input/ Output Organization

Input/output architecture is an interface to the outside world that provide systematic

means of controlling interaction with outside world. Input device such as keyboard,

scanner, digital camera etc. Output devices examples such as display, printer etc. A

general-purpose computer should have the ability to exchange information with a wide

range of devices in varying environments. Computers can communicate with other

computers over the Internet and access information around the globe. They are an

integral part of home appliances, manufacturing equipment, transportation systems,

banking and point-of-sale terminals. In this chapter, we study the various ways in

which I/O operations are performed.

A single-bus structure

5.1 Peripheral devices

Input or output devices that are connected to computer are called peripheral devices.

These devices are designed to read information into or out of the memory unit upon

command from the CPU and are considered to be the part of computer system. These

devices are also called peripherals.

96 Computer Hardware and Architecture

In addition to the processor and a set of memory modules, the third key element of a

computer system is a set of input-output subsystem referred to as I/O, provides an

efficient mode of communication between the central system and the outside

environment. Programs and data must be entered into computer memory for processing

and results obtained from computations must be recorded or displayed for the user.

Devices that are under the direct control of the computer are said to be connected

online. These devices are designed to read information into or out of the memory unit

upon command from CPU. Input or output devices attached to the computer are also

called peripherals.

We can broadly classify peripheral devices into three categories:

 Human Readable: Communicating with the computer users, e.g. video display

terminal, printers etc.

 Machine Readable: Communicating with equipments, e.g. magnetic disk,

magnetic tape, sensor, actuators used in robotics etc.

 Communication: Communicating with remote devices means exchanging data

with that, e.g. modem, NIC (network interface Card) etc.

5.2 I/O Interfacing

There are various communication devices like the keyboard, mouse, printer, etc. So,

we need to interface the keyboard and other devices with the microprocessor by using

latches and buffers. This type of interfacing is known as I/O interfacing.

Computer Hardware and Architecture 97

Block Diagram of Memory and I/O Interfacing

8085 Interfacing Pins

Following is the list of 8085 pins used for interfacing with other devices −

 A15 - A8 (Higher Address Bus)

 AD7 - AD0(Lower Address/Data Bus)

 ALE

 RD

 WR

 READY

5.3 I/O Technique

It is the technique of communication between memory and I/O devices. I/O techniques

are categorized in three types based on how information is transfers between memory

and I/O devices that whether it is using CPU interaction or Interrupt interaction.

Types of I/O technique are as follows:

Programmed I/O

Interrupt I/O

Direct Memory Access (DMA)

5.3.1 Programmed I/O

It involves CPU intervention in communication between CPU and memory. When

98 Computer Hardware and Architecture

CPU is executing a program and if encounter an instruction related to I/O operation,

CPU executes that instruction by issuing command to I/O module. I/O module will

perform the request action and then set the appropriate bits in the I/O status

registers.However, this is time consuming process that keeps the CPU busy

unnecessary. In this case CPU and memory access the same system bus. The CPU

access specific device using two different methods and they are as follows:

Memory mapped I/O – In this technique only single read and write line for memory

and I/O module read/write operation. Memory devices and I/O devices are accessed

by same instruction.

5.3.2 Interrupt- initiated I/O

Since in the above case we saw the CPU is kept busy unnecessarily. This situation can

very well be avoided by using an interrupt driven method for data transfer. By using

interrupt facility and special commands to inform the interface to issue an interrupt

request signal whenever data is available from any device. In the meantime the CPU

can proceed for any other program execution. The interface meanwhile keeps

monitoring the device. Whenever it is determined that the device is ready for data

transfer it initiates an interrupt request signal to the computer. Upon detection of an

external interrupt signal the CPU stops momentarily the task that it was already

performing, branches to the service program to process the I/O transfer, and then return

to the task it was originally performing.

5.3.3 Direct Memory Access

The data transfer between a fast storage media such as magnetic disk and memory unit

is limited by the speed of the CPU. Thus we can allow the peripherals directly

communicate with each other using the memory buses, removing the intervention of

the CPU. This type of data transfer technique is known as DMA or direct memory

access. During DMA the CPU is idle and it has no control over the memory buses. The

DMA controller takes over the buses to manage the transfer directly between the I/O

devices and the memory unit.

Computer Hardware and Architecture 99

Bus Request : It is used by the DMA controller to request the CPU to relinquish the

control of the buses.

Bus Grant : It is activated by the CPU to Inform the external DMA controller that the

buses are in high impedance state and the requesting DMA can take control of the

buses. Once the DMA has taken the control of the buses it transfers the data. This

transfer can take place in many ways.

5.4 I/0 Processor

An input-output processor (IOP) is a processor with direct memory access capability.

In this, the computer system is divided into a memory unit and number of processors.

Each IOP controls and manage the input-output tasks. The IOP is similar to CPU

except that it handles only the details of I/O processing. The IOP can fetch and execute

its own instructions. These IOP instructions are designed to manage I/O transfers only.

Below is a block diagram of a computer along with various I/O Processors. The

memory unit occupies the central position and can communicate with each processor.

The CPU processes the data required for solving the computational tasks. The IOP

provides a path for transfer of data between peripherals and memory. The CPU assigns

the task of initiating the I/O program. The IOP operates independent from CPU and

transfer data between peripherals and memory.

100 Computer Hardware and Architecture

The communication between the IOP and the devices is similar to the program control

method of transfer. And the communication with the memory is similar to the direct

memory access method. In large scale computers, each processor is independent of

other processors and any processor can initiate the operation.

The CPU can act as master and the IOP act as slave processor. The CPU assigns the

task of initiating operations but it is the IOP, who executes the instructions, and not

the CPU. CPU instructions provide operations to start an I/O transfer. The IOP asks

for CPU through interrupt. Instructions that are read from memory by an IOP are also

called commands to distinguish them from instructions that are read by CPU.

Commands are prepared by programmers and are stored in memory. Command words

make the program for IOP. CPU informs the IOP where to find the commands in

memory.

5.5 I/O Ports : A port is a physical docking point using which an external device can

be connected to the computer. It can also be programmatic docking point through

which information flows from a program to the computer or over the Internet.

Characteristics of Ports

A port has the following characteristics −

 External devices are connected to a computer using cables and ports.

 Ports are slots on the motherboard into which a cable of external device is

plugged in.

 Examples of external devices attached via ports are the mouse, keyboard,

monitor, microphone, speakers, etc.

Computer Hardware and Architecture 101

Serial Port

 Used for external modems and older computer mouse

 Two versions − 9 pin, 25 pin model

 Data travels at 115 kilobits per second

Parallel Port

The parallel port, also known as the LPT (Line Printer) port, was originally designed

for use with parallel printers.

 Used for scanners and printers

102 Computer Hardware and Architecture

 Also called printer port

 25 pin model

 IEEE 1284-compliant Centronics port

High Definition Multimedia Interface(HDMI)

HDMI is a connector and cable capable of transmitting high-quality and high-

bandwidth streams of audio and video between devices. The HDMI technology is used

with devices such as an HDTV, Projector, DVD player, or Blu-ray player. The picture

is an example of an HDMI cable from Media bridge.

HDMI cable information

The HDMI standard was developed by multiple companies, including Hitachi, Philips,

Sony, and Toshiba. A single HDMI cable replaces the three composite audio/video

cables, making it easier to connect two devices together for transmitting audio and

video signals. HDMI is capable of transmitting standard, enhanced, and high-

definition video signals, as well as up to 8-channels of digital audio signals.

Video Graphics Adapter (VGA): Short for Video Graphics Adapter or Video

Graphics Array, VGA is a popular display standard developed by IBM and introduced

Computer Hardware and Architecture 103

in 1987. VGA provides 640 x 480 resolution color display screens with a refresh rate

of 60 Hz and 16 colors displayed at a time. If the resolution is lowered to 320 x 200,

256 colors are shown. VGA utilizes analog signals, which means it is only capable of

lower resolutions and lower quality display on screens.

The VGA connector is used for display devices and is used to connect a computer to

a monitor, projector, or TV.

The illustration shows the 15-pin VGA connector, its pin assignments, and size

dimensions. As can be seen, the VGA connector has 15 holes and each hole (pin) has

its own function as explained in the below chart. A rectangle with two lines on the left

and right side is a symbol used to represent the VGA connector on many computers

and devices.

Universal Serial Bus (USB): USB is brief for Universal Serial Bus, which is an

industry standard that establishes specifications for cables and connectors for

connection and power supply between computers, peripheral devices and other storage

devices. The USB standard was released in the year of 1996, currently maintained by

104 Computer Hardware and Architecture

the USB Implementers Forum. There have been three generations of USB

specifications: USB 1.0, USB 2.0 and USB 3.0. And the USB 2.0 and USB 3.0 are

commonly used on various electric devices.

USB 2.0:

USB 2.0 was released in the year 2000, which is also referred to as Hi-Speed USB. It

is the most common version of the USB standard that we use every day. The maximum

transfer speed of USB 2.0 device is up to 480 Mbps. Nowadays, USB 2.0 is being

replaced by 3.0 in many high-end motherboards.

USB 3.0

USB 3.0 was released in November 2008, which is the third major version of the

Universal Serial Bus standard for interfacing computers and electronic devices. USB

3.0 has gradually become the new standard for USB devices by providing a lot of

improvements over USB 2.0.The major one is the data transfer rate. The data transfer

rate of USB 3.0 is up to 5 Gbit/s, which is about 10 times faster than the USB 2.0

standard. These types of USB are distinguishable by their blue colored inserts and

usually equipped with a 3.0 logo.

Computer Hardware and Architecture 105

UNIT - 6

Mobile Computing

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

Content Elaboration

Mobile Computing

6.1 Concept of Mobile Computing

Mobile Computing is a technology that allows transmission of data, voice and video

via a computer or any other wireless enabled device without having to be connected to

a fixed physical link. The main concept involves −

 Mobile communication

 Mobile hardware

 Mobile software

Mobile communication

The mobile communication in this case, refers to the infrastructure put in place to

ensure that seamless and reliable communication goes on. These would include

devices such as protocols, services, bandwidth, and portals necessary to facilitate and

support the stated services. The data format is also defined at this stage. This ensures

that there is no collision with other existing systems which offer the same service.

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Since the media is unguided/unbounded, the overlaying infrastructure is basically

radio wave-oriented. That is, the signals are carried over the air to intended devices

that are capable of receiving and sending similar kinds of signals.

Mobile Hardware

Mobile hardware includes mobile devices or device components that receive or access

the service of mobility. They would range from portable laptops, smartphones, tablet

Pc's, Personal Digital Assistants.

These devices will have a receptor medium that is capable of sensing and receiving

signals. These devices are configured to operate in full- duplex, whereby they are

capable of sending and receiving signals at the same time. They don't have to wait until

one device has finished communicating for the other device to initiate

communications.

Above mentioned devices use an existing and established network to operate on. In

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most cases, it would be a wireless network.

Mobile software

Mobile software is the actual program that runs on the mobile hardware. It deals with

the characteristics and requirements of mobile applications. This is the engine of the

mobile device. In other terms, it is the operating system of the appliance. It's the

essential component that operates the mobile device.

Since portability is the main factor, this type of computing ensures that users are not

tied or pinned to a single physical location, but are able to operate from anywhere. It

incorporates all aspects of wireless communications.

6.2 Architecture of Mobile Computing

Architecture consists of two parts

Radio Network

PCS users carry mobile stations (MS) to communicate with a BS in a PCS n/w. MS is

also referred to as handset or mobile phone. The radio coverage of a base station is

called cell. In GSM n/w each cell is controlled by BSC which are connected to MS

through BS. The BSCs are connected to MSC by landlines. Wireline Transport

Network

An MSC is a telephone exchange configured specially for mobile applications. It

interfaces the MSC (via BS) with PSTN. MSCs are also connected with mobility

database to track the location of MS and roaming management. The databases are HLR

& VLR. HLR contains the authentication information like IMSI (International Mobile

Subscriber Identity), identification information like name, address of the subscriber,

billing information like prepaid or postpaid, operator selection, denial of service to a

subscriber etc. VLR gives information about the location area of the subscriber while

on roaming and power off status of the handset.

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PCS network Architecture

GSM(Global System for Mobile Communication)

The first GSM network was launched in 1991 by Radioing in Finland with joint

technical infrastructure maintenance from Ericsson. The proposed GSM system had to

meet certain business objectives:

 Support for International Roaming

 Good Speech Quality

 Ability to support handheld terminals

 Low terminal and service cost.

 Spectral Efficiency

GSM uses a combination of FDMA and TDMA. The GSM system has an allocation

of 50 MHz bandwidth in the 900 MHz frequency band. Using FMA, this band is

divided into 124 channels each with a carrier bandwidth of 200 KHz. Using TDMA,

each of these channels is further divided into 8 time slots. Therefore with combination

of FDMA and TDMA we can realize a maximum of 992 channels for transmit and

receive. Cell: Cell is the basic service area: one BTS covers one cell. Each cell is given

a Cell Global Identity (CGI), a number that uniquely identifies the cell. Location Area:

A group of cells form a Location Area. This is the area that is paged when a subscriber

gets an incoming call. Each Location Area is assigned a Location Area Identity (LAI).

Each Location Area is served by one or more BSCs.

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GSM Architecture Overview

Abbreviations

MSC: Mobile switching center BSC : Base station controller BTS : Base transceiver

station TRX : Transceiver. MS : Mobile station OMC: Operations and Maintenance

centre. PSTN : Public switched telephone network. BSS : Base station sub-system.

HLR : Home location register VLR : Visitor locations register

6.3 Mobile Applications and Operating Software

A mobile application, most commonly referred to as an app, is a type of application

software designed to run on a mobile device, such as a smartphone or tablet computer.

Mobile applications frequently serve to provide users with similar services to those

accessed on PCs. Apps are generally small, individual software units with limited

function. This use of app software was originally popularized by Apple Inc. and its

App Store, which offers thousands of applications for the iPhone, iPad and iPod

Touch.A mobile application also may be known as an app, web app, online app, iPhone

app or smartphone app.

Mobile App Functions

The purposes of these apps run the gamut, from utility, productivity, and navigation to

entertainment, sports, fitness, and just about any others imaginable. Social media is

110 Computer Hardware and Architecture

one of the most popular fields of mobile app development and adoption. In

fact, Facebook was the most widely used app in 2017 across all platforms. Many

online entities have both mobile websites and mobile apps. In general, the difference

lies in purpose: An app is usually smaller in scope than a mobile website, offers more

interactivity, and presents more specific information in a format that's easy and

intuitive to use on a mobile device.

Different Between Mobile Apps From Regular Apps

Many mobile apps have corresponding programs meant to run on desktop computers.

Mobile apps have to work with different constraints than their desktop equivalents,

however. Mobile devices have a wide range of screen sizes, memory capacities,

processor capabilities, graphical interfaces, buttons, and touch functions, and

developers must accommodate them all. For example, mobile app users (like website

visitors) don't want to scroll sideways to see text, images, or interactive touch points,

nor do they want to struggle reading tiny text. An additional consideration for mobile

app developers is the touch interface common to mobile devices.

As of 2019, the three major players in the mobile apps space are:

 Google Play: for Android devices

 Apple's App Store: for iPads and iPhones

 Amazon AppStore: for Amazon Fire devices

Many websites also offer corresponding apps and provide download links.Installation

is fast and easy: Simply navigate to the appropriate store, find the app you want, and

download it. Your device will install it automatically once the download completes.

Mobile Operating System (Mobile OS)

Much like the Linux or Windows operating system controls your desktop or laptop

computer, a mobile operating system is the software platform on top of which other

programs can run on mobile devices. The operating system is responsible for

determining the functions and features available on your device, such as thumb wheel,

keyboards, WAP, synchronization with applications, email, text messaging and more.

The mobile OS will also determine which third-party applications (mobile apps) can

be used on your device.

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Types of Mobile Operating Systems

When you purchase a mobile device the manufacturer will have chosen the operating

system for that specific device. Often, you will want to learn about the mobile

operating system before you purchase a device to ensure compatibility and support for

the mobile applications you want to use.

Popular Mobile Operating Systems

1. Android OS (Google Inc.)

The Android mobile operating system is Google's open and free software stack that

includes an operating system, middleware and also key applications for use on mobile

devices, including smartphones. Updates for the open source Android mobile

operating system have been developed under "dessert-inspired" version

names (Cupcake, Donut, Eclair, Gingerbread, Honeycomb, Ice Cream Sandwich) with

each new version arriving in alphabetical order with new enhancements and

improvements.

2. Bada (Samsung Electronics)

Bada is a proprietary Samsung mobile OS that was first launched in 2010. The

Samsung Wave was the first smartphone to use this mobile OS. Bada provides mobile

features such as multipoint-touch, 3D graphics and of course, application downloads

and installation.

3. BlackBerry OS (Research In Motion)

The BlackBerry OS is a proprietary mobile operating system developed by Research

In Motion for use on the company’s popular BlackBerry handheld devices. The

BlackBerry platform is popular with corporate users as it offers synchronization with

Microsoft Exchange, Lotus Domino, Novell GroupWise email and other business

software, when used with the BlackBerry Enterprise Server.

4. iPhone OS / iOS (Apple)

Apple's iPhone OS was originally developed for use on its iPhone devices. Now, the

mobile operating system is referred to as iOS and is supported on a number of Apple

devices including the iPhone, iPad, iPad 2 and iPod Touch. The iOS mobile operating

system is available only on Apple's own manufactured devices as the company does

112 Computer Hardware and Architecture

not license the OS for third-party hardware. Apple iOS is derived from Apple's Mac

OS X operating system.

5. MeeGo OS (Nokia and Intel)

A joint open source mobile operating system which is the result of merging two

products based on open source technologies: Maemo (Nokia) and Moblin

(Intel). MeeGo is a mobile OS designed to work on a number of devices including

smartphones, netbooks, tablets, in-vehicle information systems and various devices

using Intel Atom and ARMv7 architectures.

6. Palm OS (Garnet OS)

The Palm OS is a proprietary mobile operating system (PDA operating system) that

was originally released in 1996 on the Pilot 1000 handheld. Newer versions of the

Palm OS have added support for expansion ports, new processors, external memory

cards, improved security and support for ARM processors and smartphones. Palm OS

5 was extended to provide support for a broad range of screen resolutions, wireless

connections and enhanced multimedia capabilities and is called Garnet OS.

7. Symbian OS (Nokia)

Symbian is a mobile operating system (OS) targeted at mobile phones that offers a

high-level of integration with communication and personal information management

(PIM) functionality. Symbian OS combines middleware with wireless

communications through an integrated mailbox and the integration of Java and PIM

functionality (agenda and contacts). Nokia has made the Symbian platform available

under an alternative, open and direct model, to work with some OEMs and the small

community of platform development collaborators. Nokia does not maintain Symbian

as an open source development project.

8. webOS (Palm/HP)

WebOS is a mobile operating system that runs on the Linux kernel. WebOS was

initially developed by Palm as the successor to its Palm OS mobile operating system.

It is a proprietary Mobile OS which was eventually acquired by HP and now referred

to as webOS (lower-case w) in HP literature. HP uses webOS in a number of devices

including several smartphones and HP TouchPads. HP has pushed its webOS into the

Computer Hardware and Architecture 113

enterprise mobile market by focusing on improving security features and management

with the release of webOS 3.x. HP has also announced plans for a version of webOS

to run within the Microsoft Windows operating system and to be installed on all HP

desktop and notebook computers in 2012.

9. Windows Mobile (Windows Phone)

Windows Mobile is Microsoft's mobile operating system used in smartphones and

mobile devices – with or without touchscreens. The Mobile OS is based on the

Windows CE 5.2 kernel. In 2010 Microsoft announced a new smartphone platform

called Windows Phone 7.

6.4 Latest Trends in Mobile Computing

Over 1 billion smartphones and 179 billion mobile applications downloaded per year,

mobile development is certainly one of the innovative and actively growing sector.

The mobile application market is arguably dominated by Google apps (Gmail, Maps,

Search), Social media (Facebook, Instagram, Twitter, Youtube) and Gaming apps

(Angry birds, Temple Run). Giants like Walmart, Bank of America and Amazon are

using mobile applications for branding, improving customer engagement, direct

marketing etc. Small and midsize businesses are also following the mobile trend.

Ultimately an effective mobile strategy involves more than just a mobile-friendly

website. Mobile application development is driven by advancements in technology

which requires businesses to have a vision for next few years. Below are some of the

trends which will determine the future of mobile application development.

1. WEARABLE DEVICES

According to IDC, 101.9 million wearable devices were shipped in 2016, up by a

strong 29 percent from the 79 million units shipped in 2015. Smart wearables like the

Apple Watch and Microsoft’s Hololens shows an upcoming change in computing and

the transition from basic to smart wearables. This opens up new opportunities for

vendors, app developers, and accessory makers. The smartphone will become the hub

of a personal-area network consisting of wearable gadgets such as on-body healthcare

sensors, smart jewellery, smart watches, display devices (like Google Glass) and a

variety of sensors embedded in clothes and shoes. These gadgets will communicate

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with mobile applications to deliver information in new ways. And will enable a wide

range of products and services in areas such as sport, fitness, fashion, hobbies and

healthcare. Thus, wearable devices connected with smartphones will influence the next

generation of mobile application development strategies.

2. INTERNET OF THINGS AND MOBILE-CONNECTED SMART

OBJECTS

Gartner says there will be 26 billion connected devices by 2020 which includes several

hundred smart objects such as LED light bulbs, toys, domestic appliances, sports

equipment, medical devices and controllable power sockets etc. These domestic smart

objects will be a part of the Internet of Things and will communicate through an App

on a smartphone or tablet. Smartphones and tablets will act as remote controls,

displaying and analyzing information, interfacing with social networks to monitor

“things” that can tweet or post, paying for subscription services, ordering replacement

consumables and updating object firmware. Established companies such as Microsoft,

with its Intelligent Systems Service, and enterprise software vendors likes SAP, with

its Internet of Things Solutions, are also adding Internet of Things capabilities to their

offerings.

Currently RiotOS and Thingsquare Mist are software technologies and RFID, WiFi,

EnOcean etc are communication technologies used for IoT. Google has two projects

Nest and Brillo specifically targeting IoT. Nest develops home automation products-

smoke alarm, camera, and thermostat, whereas Brillo is an IoT operating system which

supports Wi-Fi, Bluetooth Low Energy, and other Android things. Apple recently

launched some products of ‘Homekit’ that will enable you to have wireless and

electronic control of your household appliances. The products include light dimmers,

air monitors, a thermostat, and an entire smart home hub which can be controlled

through apps and Siri, allowing homes to be automated by voice command. On the

similar lines, Amazon launched ‘Amazon Echo’ which is a voice command device for

answering questions, playing music and controlling smart devices. A comprehensive

list of technologies driving IoT can be found at the Posts capes labs.

3. M-COMMERCE

Various analysts believe positive trend in mobile purchases will continue over the next

Computer Hardware and Architecture 115

4 years as more and more consumers adapt to m-commerce. Increasing popularity of

Apple Pay and Google Wallet will facilitate purchases using the mobile phones instead

of debit or credit cards. This will require developers to build a mobile application that

can process transactions without the need of physical debit/credit cards or cash.

Coupled with wearables that can process payments m-commerce will take a different

shape. Beyond data collection and predictive analytics, wearables will also play a key

role in the future of mobile payments and customer loyalty.

4. MOTION AND LOCATION SENSING

Most mobile phones have location sensor capabilities which use multiple positioning

methods to provide different granularities of location data. Knowing an individual’s

location to within a few meters is useful for providing highly relevant contextual

information and services. Motion sensing apps are used in security, anti-theft, power-

saving and games. Location sensing is useful in Geotagging, Games, Vehicle

navigation, and fitness apps. Apps exploiting precise indoor location currently use

technologies such as Wi-Fi, imaging, ultrasonic beacons, and geomagnetic. In the

longer run technologies such as smart lighting will also become important. Precise

indoor location sensing, combined with mobile applications, will enable a new

generation of extremely personalized services and information.

5. INNOVATIVE MOBILE USER EXPERIENCE DESIGN

Effective display of data and content on your mobile user interface is important for a

sound user experience. Successful mobile application companies, such as Houzz,

Instagram, Pinterest, and Wunderlist, have developed new patterns depicting intuitive

designs and interactive interfaces. Designers are also creating apps that can

accommodate mobile challenges, such as partial user attention and interruption. Apps

should exploit technologies with novel features such as interactive content layers,

circular design pattern, cards and manipulation of content. These features create an

“augmented reality” by allowing the users to interact with the content in further detail.

Leading consumer apps are setting high standards for user interface design, and all

organizations must master new skills and work with new partners to meet growing user

expectations.

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6. APPLICATION PERFORMANCE MANAGEMENT (APM)

There are two factors which lead to performance bottlenecks in app testing i.e.

diversity of mobile devices and the non-deterministic nature of mobile networks. But

mobile metrics and monitoring tools collectively known as Application Performance

Management (APM) has improved the testing and quality assurance. APM provides

visibility into app behavior, delivers statistics about which devices and OSs are

adopted, and monitors user behavior to determine which app features are being

successfully exploited. With the application landscape and enterprise infrastructures

shifting to the cloud, APM tools face increased challenges to provide real performance

benefits across systems with virtual perimeters. Modern enterprises require robust

tools that can monitor resources used by applications, correlate that data with

meaningful user insights, and align performance with business processes.

7. ENTERPRISE MOBILE MANAGEMENT

Enterprise mobile management (EMM) is a set of people, processes, and technology

using mobile computing for streamlining businesses. The main dimensions of EMM

are security, application management, and financial management. It also includes

mobile device management, mobile application management, application wrapping

and containerization, and some elements of enterprise file synchronization and sharing.

Such tools will mature, grow in scope and eventually address a wide range of mobile

management needs across all popular Operating Systems on smartphones, tablets, and

PCs. Thus, EMM represents the future evolution and convergence of several mobile

management, security, and support technologies.

We cannot deny that mobile applications have become an integral element of the

digital ecosystem. The skills required in building consumer apps are in greater demand

than ever now compelling businesses to take mobility seriously. Businesses should

keep an eye on these trends to align their mobile application development strategies.

Computer Hardware and Architecture 117

References:

https://www.tutorialspoint.com/microprocessor/microprocessor_io_interfacing_over

view.htm

https://www.geeksforgeeks.org/io-interface-interrupt-dma-mode/

https://www.studytonight.com/computer-architecture/input-output-processor

https://www.computerhope.com/jargon/v/vga.htm

https://www.lifewire.com/what-is-a-mobile-application-2373354

118 Computer Hardware and Architecture

UNIT - 7

Computer Assembly

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

7.1 Identify Different Components of a Computer

Mother Board

The main printed circuit board in a computer is known as the motherboard. Other

names for this central computer unit are system board, mainboard, or printed wired

board (PWB). The motherboard is sometimes shortened to Mobo. Numerous major

components, crucial for the functioning of the computer, are attached to the

motherboard. These include the processor, memory, and expansion slots. The

motherboard connects directly or indirectly to every part of the PC. The type of

motherboard installed in a PC has a great effect on a computer's system speed and

expansion capabilities.

Identifying through Windows or another utility

You can view the manufacturer and model number in your Windows system using

the System Information utility. To access this utility, follow the steps below.

Windows 10 & Windows 8

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1. On the Windows desktop screen, press Windows key + X to open the Power

User Task Menu.

2. Select the Run option in the menu.

3. In the Run text field, type msinfo32 and press Enter.

Windows 7 and earlier versions

1. Open the Start menu.

2. Click on All Programs > Accessories > System Tools, then select the System

Information utility.

Power Supply

Abbreviated as PS or P/S, a power supply or PSU (power supply unit) is a hardware

component of a computer that supplies all other components with power. The power

supply converts a 110-115 or 220-230 volt AC (alternating current) into a steady low-

voltage DC (direct current) usable by the computer and rated by the number of watts

it generates. The image shows an Antec True 330, a 330 Watt power supply.

The power supply is located at the back of the computer, usually at the top. However,

many more recent tower computer cases house the power supply at the bottom., the

power supply is usually located at the top back or bottom back of the case. In a desktop

computer case (all-in-one), the power supply is located at the back left or back right.

Parts found on the back of a power supply

Below is a list of parts you may find on the back of the power supply.

 A connection for the power cord to the computer.A fan opening to heat out of

the power supply.

 A red switch to change the power supply voltage.

 A rocker switch to turn the power supply on and off.

120 Computer Hardware and Architecture

On the front of the power supply, which is not visible unless the computer is opened,

you will find several cables. These cables connect to the computer motherboard and

other internal components. A power supply connects to the motherboard using an ATX

style connector and may have one or more of the following cables to connect power to

other devices.

 Auxiliary connector

 Berg connector

 Molex connector

 P4 connector

Processor

Every computer contains at least one processor, also known as a CPU or central

processing unit. Your computer’s CPU is probably made by Intel or AMD. Here

is how to see what CPU you have and how fast it is. You don’t need a system

information utility to find this information. Windows shows it in several different

places.

To find this information in Windows 10’s Settings app, navigate to

Settings > System > About.

Look under “Device specifications.” The name of your computer’s processor and its

speed are displayed to the right of “Processor.” You can press Windows+i to open the

Settings app quickly. You can also press the Windows key, type “About” to search

your Start menu for this settings screen, and click the “About This PC” shortcut that

appears.

Computer Hardware and Architecture 121

Windows 10’s Task Manager shows detailed CPU information, too. Right-click your

taskbar and select “Task Manager” or press Ctrl+Shift+Esc to launch it. Click the

“Performance” tab and select “CPU.” The name and speed of your computer’s CPU

appear here. (If you don’t see the Performance tab, click “More Details.”) You’ll also

see real-time CPU usage data and other details, including the number of cores your

computer’s CPU has.

Windows 7—or Windows 10—users can find this information in the Control Panel.

Specifically, it’s on the system pane. Head to Control Panel > System and Security >

System to open it. You can also press Windows+Pause on your keyboard to instantly

122 Computer Hardware and Architecture

open this window. Your computer’s CPU model and speed are displayed to the right

of “Processor” under the System heading.

If Windows isn’t booting on your system, you can still find this information in several

other ways. Your computer’s documentation likely includes system specification

details like this. You may also find this information displayed in your

computer’s BIOS or UEFI firmware settings screen.

Memory : To find out information about your computer's memory, you can look at

the settings in Windows. Just open up the Control Panel and click on System and

Security. There should be a subheading called View amount of RAM and processor

speed'. When you click on this option, it will show you information such as memory

size, OS type, and processor model and speed.

However, this will not tell you anything about RAM speed. To get this information,

you need a third-party program such as CPUID's CPU-Z software. Once this is

installed and it has scanned your system, it can show you more information about your

Computer Hardware and Architecture 123

computer, laid out in easy-to-navigate tabs.

Input/Output Devices

Brief Explanation of Input Devices

Keyboard: A computer or laptop keyboard is kind of hardware device that you can

use to type data in a computer system. It usually plugs and play device. A computer

keyboard includes a set of alphabets (A-Z), numbers (0-9), symbols and function keys.

A computer keyboard type should be PS/2 (5-Pin DIN or 6-Pin DIN), USB (Universal

Serial Bus), Wireless. Now days USB and Wireless keyboard are common in use.

Earlier, PS/2 was the most used keyboard.

Mouse: A computer mouse is an input and a hardware, pointing device that you can

connect to your computer system. You can move cursor on your screen. It’s a hand

held device that you can move with your hand and do clicks (right or left) on your

screen to send commands to your computer screen area. Earlier PS/2 mouse was in

existence but now a days USB and Wireless Mouse have taken place.

124 Computer Hardware and Architecture

In the memory tab, you can find out the number of slots your computer has, what type

of memory, how big the memory is and what frequency it runs at. There will also be

information about memory latency and clock speed.

Touchpad: A touchpad or trackpad is a kind of input device that has a limited area

wherein you can Point, scroll, click and swipe. A Touchpad most commonly found on

computer laptops (computer brand doesn’t matter). Touchpad allows to use all the

features as you do with a computer mouse.

TrackPoint: Most commonly TrackPoint found in IBM ThinkPad Notebook

computers, and originally introduced by IBM in 1992. TrackPoint is a cursor control

device that’s built between laptop keyboard and also known as pointing stick. Now the

days touchpad method is in existence.

Scanner: A scanner is an electronic and input device that allows user to scan any of

document, images, etc. and convert them to digital formats that you can see on your

computer screen. It’s a kind of hardware device that you can connect to your desktop

Computer Hardware and Architecture 125

computer/laptop by using USB connection. Most uses in offices to create an image

files of physical documents.

Microphone: Also knows as its common name “Mic”. Basically Microphone converts

your voice/sound into electrical signals and you will get an output on connected

speakers. Can be used to record voice.

Barcode Reader: A Barcode Reader is an input device and also known as Barcode

Scanner is a hand held device. It is an electronic device that can read barcodes those

has printed on any product, etc. It is generally used to track products and prices in a

computer software system.

Joystick: Joystick is a kind of control stick that most used for computer gaming’s that

allows users to control characters or machine.

126 Computer Hardware and Architecture

Webcam: Webcam is a short form of Web Camera is an input device. It should be

connected to computer directly or indirectly. It allows users to stream live video

calling, take pictures, etc.

Output Devices

Printers: A printer is an output device that can print any document, web page,

photographs, etc by command send by your computer desktop or laptop. There are

several brands and type of printers available for an example: Laser-jet, Office jet, Ink

jet, Line printers. Now days most of the printers includes the feature of scanner and

copier.

Projector: A projector is a hardware device that you can connected to computer

desktop/laptop by using HDMI or VGA cable (depends compatibility) to project your

computer display in a large screen. If you are using a projector, you also required a

projection screen where you can project the computer display.

Computer Hardware and Architecture 127

Plotters: A Plotter is a big size printer that allow users to get big size print that cannot

be done by basic printers. Most of the plotter has the feature of LTP, LAN and USB

printing ports that connectivity to your computer. Generally, plotters are used to take

prints of line-art application, big maps, architecture designs, drawings, etc.

Monitor: In computing, a monitor screen is a computer display. A monitor could be a

CRT, LED or LCD. Whatever you do in your computer, monitor is the hardware

device that shows you the output. So, without monitor you can’t work in your

computer.

Speakers: Computer speaker is an output device because you are getting sound from

it whenever you play any online or offline music, video or anything that has sound in

it. Basically, speaker is a hardware device that you can connect to your computer to

generate sound.

128 Computer Hardware and Architecture

Printer and Ports

If the printer has failed to respond to a print command, the printer driver port may not

have been configured correctly. A port is an interface channel used for transferring

data from the computer to a printer. In order to communicate and print successfully,

the port setting in the printer driver software must be set correctly.Some users may

receive an error message that indicates an issue with the port settings. For example, if

you are using a printer via a USB or network connection and receive the error message

"There was an error writing to LPT1", this would indicate that the print data has been

sent to a port that Windows reserves for printers connected via a Parallel interface.

In order to determine if the port is set correctly, we recommend checking the printer

port setting in the printer driver and changing it if necessary. However, we recommend

that you first follow the guidance in the following Related Article, returning to this

article if advised to do so:

 Troubleshooting Printer-related Communication Issues in Windows

 Open the Printers folder and confirm the current port setting in the printer driver

 Check the printer port setting is correct

 Adding the printer port for network printers

Figure 2: In this example, the printer port has been changed by selecting a USB Virtual

printer port (e.g. USB001).

 Make sure that a sheet of plain A4 paper is loaded into the printer's paper tray.

Computer Hardware and Architecture 129

Try to print a Test Page from the Printer Properties > General tab. Click on Print

Test Page from the bottom of the window:

 Using the Test Page function is a good way to test the communication between

the printer and computer.

7.2 Mother Board ( form factor)

The shape and layout of a motherboard is called the form factor. The form factor

affects where individual components go and the shape of the computer's case. There

are several specific form factors that most PC motherboards use so that they can all fit

in standard cases. The form factor is just one of the many standards that apply to

motherboards. Some of the other standards include:

 The socket for the microprocessor determines what kind of Central Processing

Unit (CPU) the motherboard uses.

 The chipset is part of the motherboard's logic system and is usually made of two

parts -- the northbridge and the southbridge. These two "bridges" connect the

CPU to other parts of the computer.

 The Basic Input/Output System (BIOS) chip controls the most basic functions

130 Computer Hardware and Architecture

of the computer and performs a self-test every time you turn it on. Some systems

feature dual BIOS, which provides a backup in case one fails or in case of error

during updating.

 The real time clock chip is a battery-operated chip that maintains basic settings

and the system time.

The slots and ports found on a motherboard include:

 Peripheral Component Interconnect (PCI)- connections for video, sound and

video capture cards, as well as network cards

 Accelerated Graphics Port (AGP) - dedicated port for video cards.

 Integrated Drive Electronics (IDE) - interfaces for the hard drives

 Universal Serial Bus or FireWire - external peripherals

 Memory slots

Some motherboards also incorporate newer technological advances:

 Redundant Array of Independent Discs (RAID) controllers allow the computer

to recognize multiple drives as one drive. PCI Express is a newer protocol that

acts more like a network than a bus. It can eliminate the need for other ports,

including the AGP port. Rather than relying on plug-in cards, some

motherboards have on-board sound, networking, video or other peripheral

support.

Chipset

A chipset is a group of small circuits that coordinates the flow of data and instructions

between the central processing unit (CPU) or microprocessor and external devices.

This includes the CPU itself, the main memory, the secondary cache and any devices

situated on the buses. The chipset also controls data flow to and from hard disks, and

other devices connected to the IDE channels.

Chipset manufacturers include Intel, UMC, SIS, VIA, ALI, OPTI, etc.

The chipset originally was made up of a large number of electronic chips, hence the

name. A chipset generally has two components:

 The Northbridge (also called the memory controller) is in charge of controlling

Computer Hardware and Architecture 131

transfers between the processor and the RAM. That is why it is located

physically near the processor. It is sometimes called the GMCH, for Graphic and

Memory Controller Hub.

 The Southbridge (also called the input/output controller or expansion controller)

handles communications between peripheral devices. It is also called

the ICH (I/O Controller Hub). The term bridge is generally used to designate a

component which connects two buses.

Expansion Buses

An expansion bus is an assortment of wires that allows for computer expansion with

the use of an expansion board. Expansion buses give rise to expansion slots. Expansion

boards are inserted into an expansion slot on the motherboard or backplane that

provides additional features to a computer system. Buses carry signals, such as data;

memory addresses, power and control signals from component to component.

Expansion buses enhance the PCs capabilities by allowing users to add missing

features in their computers in the form of adapter cards that are slotted in expansion

slots. The different types of buses include PCI, ISA, EISA I/0 bus.

Basic Input Output System – BIOS

BIOS is a term that stands for basic input/output system. It consists of low-level

software that controls the system hardware and acts as an interface between the

operating system and the hardware. BIOS is used by the microprocessor to get the

computer started after it is turned on.

All motherboards include a small block of Read–Only Memory (ROM) which is

132 Computer Hardware and Architecture

separate from the main system memory used for loading and running software. On

PCs, the BIOS contains all the code required to control the keyboard, display screen,

disk drives, serial communications, and a number of miscellaneous functions.

The BIOS is stored on a ROM chip because ROM retains information even when no

power is being supplied to the computer. The downside of storing data in an older

computer’s ROM is that the chip has to be removed to update information. Many

modern PCs have flash BIOS, which means that the BIOS has been recorded on a flash

memory chip, which can be updated if necessary.

The BIOS is typically placed in a ROM chip that comes with the computer (it is often

called a ROM BIOS). This ensures that the BIOS will always be available and will not

be damaged by disk failures. It also makes it possible for a computer to boot itself.

Because RAM is faster than ROM, though, many computer manufacturers design

systems so that the BIOS is copied from ROM to RAM each time the computer is

booted. This is known as shadowing.

Some Bios Hardware Configuration Options That Can Be Changed

 Change the Boot Order

 Load BIOS Setup Defaults

 Remove a BIOS Password

 Create a BIOS Password

 You can change the Date and Time

 Change Floppy Drive Settings

 To change Hard Drive Settings

 Changing CD/DVD/BD Drive Settings

Computer Hardware and Architecture 133

 View Amount of Memory Installed

 Change the Boot Up NumLock Status

 Enable or Disable the Computer Logo

 Enable or Disable the Quick Power-On Self-Test (POST)

7.3 Power Supply ( SMPS Concept)

Switched-Mode Power Supply (SMPS) is an electronic circuit which converts the

power using switching devices that are turned on and off at high frequencies, and

storage components such as indicators or capacitors to supply power when the

switching device is in its non-conduction state. It can be abbreviated as SMPS. The

switched-mode power supply is also called switch-mode power supply or switching-

mode power supply. Its efficiency is high. That’s why we use it in the variety of

electronic types of equipment which require a stable and efficient power supply.

The working of SMPS is simply understood by knowing that the transistor used in LPS

is used to control the voltage drop while the transistor in SMPS is used as a controlled

switch.

Working

The working of SMPS can be understood by the following figure.

Let us try to understand what happens at each stage of SMPS circuit.

Input Stage

The AC input supply signal 50 Hz is given directly to the rectifier and filter circuit

combination without using any transformer. This output will have many variations and

the capacitance value of the capacitor should be higher to handle the input fluctuations.

This unregulated dc is given to the central switching section of SMPS.

134 Computer Hardware and Architecture

Switching Section

A fast switching device such as a Power transistor or a MOSFET is employed in this

section, which switches ON and OFF according to the variations and this output is

given to the primary of the transformer present in this section. The transformer used

here are much smaller and lighter ones unlike the ones used for 60 Hz supply. These

are much efficient and hence the power conversion ratio is higher.

Output Stage

The output signal from the switching section is again rectified and filtered, to get the

required DC voltage. This is a regulated output voltage which is then given to the

control circuit, which is a feedback circuit. The final output is obtained after

considering the feedback signal.

Control Unit

This unit is the feedback circuit which has many sections. Let us have a clear

understanding about this from The following figure.

The above figure explains the inner parts of a control unit. The output sensor senses

the signal and joins it to the control unit. The signal is isolated from the other section

so that any sudden spikes should not affect the circuitry. A reference voltage is given

as one input along with the signal to the error amplifier which is a comparator that

compares the signal with the required signal level.

By controlling the chopping frequency the final voltage level is maintained. This is

controlled by comparing the inputs given to the error amplifier, whose output helps to

decide whether to increase or decrease the chopping frequency. The PWM oscillator

produces a standard PWM wave fixed frequency.

We can get a better idea on the complete functioning of SMPS by having a look at the

Computer Hardware and Architecture 135

following figure.

The SMPS is mostly used where switching of voltages is not at all a problem and where

efficiency of the system really matters. There are few points which are to be noted

regarding SMPS. They are

 SMPS circuit is operated by switching and hence the voltages vary continuously.

 The switching device is operated in saturation or cut off mode.

 The output voltage is controlled by the switching time of the feedback circuitry.

 Switching time is adjusted by adjusting the duty cycle.

 The efficiency of SMPS is high because, instead of dissipating excess power as

heat, it continuously switches its input to control the output.

Disadvantages

There are few disadvantages in SMPS, such as

 The noise is present due to high frequency switching.

 The circuit is complex.

 It produces electromagnetic interference.

Advantages

The advantages of SMPS include,

 The efficiency is as high as 80 to 90%

 Less heat generation; less power wastage.

 Reduced harmonic feedback into the supply mains.

 The device is compact and small in size.

136 Computer Hardware and Architecture

 The manufacturing cost is reduced.

 Provision for providing the required number of voltages.

Applications

There are many applications of SMPS. They are used in the motherboard of computers,

mobile phone chargers, HVDC measurements, battery chargers, central power

distribution, motor vehicles, consumer electronics, laptops, security systems, space

stations, etc.

Types of SMPS

SMPS is the Switched Mode Power Supply circuit which is designed for obtaining the

regulated DC output voltage from an unregulated DC or AC voltage. There are four

main types of SMPS such as

 DC to DC Converter

 AC to DC Converter

 Fly back Converter

 Forward Converter

The AC to DC conversion part in the input section makes the difference between AC

to DC converter and DC to DC converter. The Fly back converter is used for Low

power applications. Also there are Buck Converter and Boost converter in the SMPS

types which decrease or increase the output voltage depending upon the requirements.

The other type of SMPS include Self-oscillating fly-back converter, Buck-boost

converter, etc.

Computer Hardware and Architecture 137

References:

https://www.computerhope.com/jargon/p/power-supply.htm

https://www.howtogeek.com/413942/how-to-see-what-cpu-is-in-your-pc-and-how-

fast-it-is/

https://pcguide4u.com/list-input-output-devices-computer/

https://www.tutorialspoint.com/electronic_circuits/electronic_circuits_smps.htm

https://www.epson.eu/viewcon/corporatesite/products/mainunits/faq/1352

https://computer.howstuffworks.com/motherboard1.htm

138 Computer Hardware and Architecture

UNIT 8

Troubleshoot and Repair Maintenance

Learning process and support material

 Class demonstration with pictures and computer sets

 Questionnaire

 Use related video from YouTube.

8.1 Mother Board (Form factor, Parts, Chipset and controller, Buses and

BIOS)

Other peripherals may spin up if the motherboard is dead, but more often nothing at

all happens when you turn on the power. No beeps, no lights, no fans, nothing. If you

think you have a dead motherboard, think again. The most likely cause of a dead

system is a blown fuse or breaker at the wall receptacle. If you're certain the system is

getting power and you have just installed the motherboard, it's much more likely that

you've neglected to connect a cable or made some other basic error than that the

motherboard itself is bad, assuming of course that the problem motherboard is a high

quality product.

EARLY WARNING SIGNS

If your computer starts to develop issues, most of the time, there are some early

warning signs that a part is going bad. Here are some things to look out for with your

motherboard:

1. Motherboard doesn’t recognize/show peripherals.

2. Peripherals will stop working for a few seconds or more.

3. Slow boot-ups could indicate that your motherboard is going bad, though it could

be other components as well (more on this below).

4. Computer won’t recognize flash drives, or monitor sometimes shows strange

lines (particularly relevant if you have onboard video on your motherboard).

5. Motherboard doesn’t POST (Power On Self Test).

6. Burning smell or burn marks anywhere on the motherboard itself.

7. Bulging or leaking capacitors

Computer Hardware and Architecture 139

SIGNS OF FAILURE

Motherboards are historically the most difficult pieces of hardware to diagnose

because, in most cases, you have to rule out every other piece of hardware that is

connected to it. There aren’t usually any real signs of failure, other than your computer

suddenly turning into an expensive doorstop. A hard drive might give you signs of

failure, such as blue screens or lost files, but a motherboard will just suddenly stop

working. That being said, here are some things you can try first to ensure the problem

is with your motherboard instead of another hardware component.

DIAGNOSING THE PROBLEM

There are some easy troubleshooting steps you can take to determine if your

motherboard is going bad. Below we break the troubleshooting procedure into two

categories: 1) What to check if the computer still passes the POST and boots (or

attempts to boot), and 2) what to check if the computer no longer passes the POST or

does not even turn on.

COMPUTER PASSES POST AND BOOTS OS

If your computer still turns on and even boots into the operating system, you should

rule out other hardware components first to make sure these aren’t causing the

symptoms listed above.

Harddrive(s): Are files taking a longer time to transfer? Are you seeing errors or

blue screens? Has boot time increased significantly? Do you hear any clicking or loud

whining noises? If the answer to any of these questions is yes, your harddrive may be

going bad. It will be worthwhile to run the diagnostic utilities in Windows and/or from

the drive’s manufacturer. Also, see our companion article on Hard Drive

140 Computer Hardware and Architecture

Failure: Warnings and Solutions.

Video: Does the display seem garbled or do you see artifacts on the screen that you

did not see before? Do graphics-intensive tasks cause blue screens or instability? If

so, your videocard may be going bad and will warrant further testing. Also, see our

guide on videocard failure symptoms for further troubleshooting.

Memory (RAM): Even though it doesn’t have any moving parts, there is a chance

that your memory could be failing and causing your system to error or become

unstable. In this case, a running a diagnostic tool such as Memtest 86 or Memtest 86

+ is recommended for further troubleshooting.

Processor (CPU): Although somewhat rare, CPU failure could be a cause of system

instability. If you have an Intel processor, downloading and running the Intel

Processor Diagnostic Tool may uncover issues with the processor itself. For AMD

processors, try the AMD system monitor tool.

Power Supply (PSU) : A failing or insufficient power supply (or one that is operating

out of spec) can quickly cause a system to become unstable and also potentially cause

damage to the other computer system components. Ensure you have the proper power

supply for your system, and double check the supply’s voltages to make sure they are

operating in line with their rated output (the voltages can easily be monitored in the

BIOS or in software utilities supplied by motherboard manufacturers). If you are still

unsure, please also read through our article on power supply troubleshooting.

There are so many wires in there.

EARLY WARNING SIGNS

If your computer starts to develop issues, most of the time, there are some early

warning signs that a part is going bad. Here are some things to look out for with your

motherboard:

1. Motherboard doesn’t recognize/show peripherals.

2. Peripherals will stop working for a few seconds or more.

3. Slow boot-ups could indicate that your motherboard is going bad, though it could

be other components as well (more on this below).

Computer Hardware and Architecture 141

4. Computer won’t recognize flash drives, or monitor sometimes shows strange

lines (particularly relevant if you have onboard video on your motherboard).

5. Motherboard doesn’t POST (Power On Self Test).

6. Burning smell or burn marks anywhere on the motherboard itself.

7. Bulging or leaking capacitors

SIGNS OF FAILURE

Motherboards are historically the most difficult pieces of hardware to diagnose

because, in most cases, you have to rule out every other piece of hardware that is

connected to it. There aren’t usually any real signs of failure, other than your computer

suddenly turning into an expensive doorstop. A hard drive might give you signs of

failure, such as blue screens or lost files, but a motherboard will just suddenly stop

working. That being said, here are some things you can try first to ensure the problem

is with your motherboard instead of another hardware component.

DIAGNOSING THE PROBLEM

There are some easy troubleshooting steps you can take to determine if your

motherboard is going bad. Below we break the troubleshooting procedure into two

categories: 1) What to check if the computer still passes the POST and boots (or

attempts to boot), and 2) what to check if the computer no longer passes the POST or

does not even turn on.

COMPUTER PASSES POST AND BOOTS OS

If your computer still turns on and even boots into the operating system, you should

rule out other hardware components first to make sure these aren’t causing the

symptoms listed above.

Harddrive(s): Are files taking a longer time to transfer? Are you seeing errors or

blue screens? Has boot time increased significantly? Do you hear any clicking or loud

whining noises? If the answer to any of these questions is yes, your hard drive may be

142 Computer Hardware and Architecture

going bad. It will be worthwhile to run the diagnostic utilities in Windows and/or from

the drive’s manufacturer. Also, see our companion article on Hard Drive

Failure: Warnings and Solutions. Video: Does the display seem garbled or do you see

artifacts on the screen that you did not see before? Do graphics-intensive tasks cause

blue screens or instability? If so, your video card may be going bad and will warrant

further testing. Also, see our guide on video card failure symptoms for further

troubleshooting.

Memory (RAM): Even though it doesn’t have any moving parts, there is a chance

that your memory could be failing and causing your system to error or become

unstable. In this case, a running a diagnostic tool such as Memtest 86 or Memtest 86

+ is recommended for further troubleshooting.

Processor (CPU): Although somewhat rare, CPU failure could be a cause of system

instability. If you have an Intel processor, downloading and running the Intel

Processor Diagnostic Tool may uncover issues with the processor itself. For AMD

processors, try the AMD system monitor tool.

Power Supply (PSU): A failing or insufficient power supply (or one that is operating

out of spec) can quickly cause a system to become unstable and also potentially cause

damage to the other computer system components. Ensure you have the proper power

supply for your system, and double check the supply’s voltages to make sure they are

operating in line with their rated output (the voltages can easily be monitored in the

BIOS or in software utilities supplied by motherboard manufacturers). If you are still

unsure, please also read through our article on power supply troubleshooting.

Motherboard BIOS Updates : Many system instabilities can be fixed by a

motherboard BIOS update (especially on newer hardware). Please consult the support

site of your motherboard’s manufacturer for more details. Finally, also a brief word on

system cooling: In many instances, errors are experienced due to improper cooling or

even cooling failure in a computer system. If any of the system’s components are

operating out of spec due to overheating, system instability can result. A visual

inspection of the system is suggested to make sure that all components are seated

properly and being cooled sufficiently (i.e. case and component fans are operating

normally). Temps can also be monitored for anomalies inside the operating system

Computer Hardware and Architecture 143

using a wide variety of tools – we suggest a few free ones you can use in our article

on PC temperature monitoring.

COMPUTER DOES NOT POST OR TURN ON

Miniature technicians working on a computer circuit board or motherboard. Tech

support concept.

If your computer doesn’t pass the POST test or even turn on, hardware failure is almost

certain. But the motherboard might still be functional. We want to make certain it’s

not some other culprit. The first to thing to do is perform a brief visual inspection on

the system itself. Are all components seated properly? If the system turns on, are all

the fans spinning? If the motherboard has a visual LED indicator, what color is it

(usually green means everything is OK)? If there is any doubt, try re-seating

components as necessary and try starting the system again. Some more modern

motherboard will even have LEDs for individual components. For instance, if there’s

a problem with your RAM or CPU, you should be able to find an LED near that

specific component, indicating if there’s a problem or not (again, green usually means

everything is OK).

The second thing to do is confirm whether the motherboard produces error (or beep)

codes when trying to start the system up with key components missing (e.g. CPU,

RAM, video). This assumes, of course, that the system still turns on. For example, if

you remove the RAM and start the computer, does it respond with error beeps? Do

note that some modern motherboards no longer support beep codes (please consult the

manual of your motherboard to make sure yours does). For more details on different

motherboard beep (error) codes and what they mean, please consult these

144 Computer Hardware and Architecture

resources here and here. In some cases it’s actually the power supply that’s bad.

Power supplies can appear to still be functioning, as the power supply fan may still

run, as well as the CPU fan and any lights that you might have on your computer. But

just because these parts activate, it doesn’t mean the power supply is supplying enough

juice to the motherboard or other parts of the computer.

The silver CMOS battery inside a motherboard. Finally, there are two more quick tests

you can perform. The first and quickest is to reset the board’s CMOS by removing the

battery. The second is to test the components outside the PC case. We have a

great step-by-step guide over on the PCMech Forums that will take you through these

steps to determine if you have a short or faulty component.

IT’S DEAD – NOW WHAT?

Unfortunately, if going through the diagnostic procedures above did not help, it may

be time for a new motherboard. There’s no real way to tell how your motherboard died.

Electronic parts experience wear and tear like anything else. All parts do eventually

die; it’s a normal thing, though sometimes motherboards can die from being shorted

out by a low-quality power supply. Again, this is something you can determine by

putting a new and hopefully higher quality power supply in your machine and seeing

if it runs or not.

If you know your motherboard is dead, as an alternate route, you could try and repair

your motherboard, but it’s no easy task. You would need a solid understanding of

electrical components, such as capacitors, for instance. You’d need to not only

understand the risk of electrical shock, but also that it’s difficult to check if a capacitor

is dead on modern motherboards. However, if you want to give it a go, Tom’s

Computer Hardware and Architecture 145

Hardware has put together an excellent and well-researched guide on replacing

capacitors.

The difference between a good capacitor and a capacitor that needs replacing.

For most people, though, they’re much better off buying a new motherboard. In this

case, its best to look for an exact replacement. If it’s too old, you might want to

consider looking into a newer motherboard for your system as long as your

components will work with it. On the other hand, it might be worth looking into

building an all-new PC if you can afford it.

8.2 Power Supply (SMPS Concept, UPS)

Switching power supply troubleshooting

1. Blown fuse

In general conditions, blown power fuse indicates problems in internal circuits. The

power supply operates under high voltage and current. Voltage fluctuations or surges

of power grid often give rise to instant increase of current, which may result in blown

power fuse. Users should check whether there is breakdown, open circuit or damage

on rectifier diode, HV filtering electrolytic capacitor, and inversion power switch tube

at the input end. If the power fuse is blown with no indication of other problems, users

need to check components on the circuit board to check whether they are burned out

with leaked electrolyte. If there is no such condition, users should check whether there

is breakdown or short circuit by multimeter. Users shall not start up the equipment

even after finding out and replacing the damaged part, because HV components with

malfunctions may damage the newly-replaced part. When dealing with blown power

fuse, users must check all HV components on the circuit board before starting up the

equipment.

146 Computer Hardware and Architecture

2. No DC output or unstable voltage output

If the power fuse remains in perfect condition but there is no DC output at various

levels in loaded condition, it may be caused by open circuit, short circuit, overvoltage,

overcurrent, failure of auxiliary power supply, failure of oscillating circuit, over load

of power supply, breakdown of rectifier diode in high-frequency rectification and

smoothing circuit, or electric leakage of smoothing capacitor. If voltage output remains

zero after checking secondary components by multimeter and clearing breakdown,

overload or short circuit of high-frequency rectifier diode, it can be confirmed there is

problem with control circuit of power supply. If there is voltage output at some parts,

that means the onboard circuit works properly and it is problem of high-frequency

rectification and smoothing circuit. High-frequency filtering circuit mainly uses

rectifier diode and low-voltage filtering capacitor to output DC. If the rectifier diode

breaks down, the circuit will be unable to output voltage. In addition, electric leakage

of filtering capacitor results in unstable voltage output. Damaged components can be

found out by checking relevant parts with a multimeter.

3. Poor load capacity

Poor load capacity is a common malfunction. It is often seen at traditional power

supplies or those which work for long hours. It is caused by aging components,

unstable switch tube, or poor cooling condition. Users shall check and confirm the

status of regulated diode, rectifier diode and HV smoothing capacitor etc.

Switching power supply repair Method

Computer Hardware and Architecture 147

Repairing the switching power supply can be processed in two steps: 1. In case of

power off, users can carry out maintenance by visual check, smelling, asking and

measuring.

 Visual check: Open shell of the power supply to check whether the power fuse

has been blown. Check internal part of the power supply. If components on PCB

are burned out, users shall check surrounding components and relevant circuit

components.

 Smelling: Check whether there is burnt smell in internal part of the power supply

and whether there is burnt-out component.

 Asking: Ask the damaging process of the power supply and check whether there

is violative operation

 Measuring: Use multi meter to measure voltage at both ends of the high-voltage

capacitor before powering on. If switching power supply fails to oscillate or

presents malfunctions caused by switch tube, in most cases the voltage at both

ends of HV filter capacitor is not released. As the voltage is really high, please

be careful! When measuring the forward and backward resistance at both ends

of AC power lines as well as charging status of capacitor, the resistance value

should not be too low, otherwise the internal part of the power supply would

present short circuit. In addition, the capacitor shall be confirmed to release and

charge power. Then, users need to measure resistance to ground of various

output ends after releasing load respectively. Normally, the indicator of the multi

meter shall swing for the power releasing or charging of capacitor. The indicator

is supposed to display resistance of the bleeder at last.

4. Powering-on test

Check whether the power fuse is blown and whether components are on smoke after

powering on. If needed, users shall cut off power to carry out maintenance.

Measure whether there is a voltage output of 300V at both ends of HV smoothing

capacitor. If it is normal, users shall check rectifier diode and smoothing capacitor etc.

Measure whether there is voltage output at secondary coil of high-frequency

transformer. If it is normal, users shall check whether switch tube is damaged, whether

the switch tube oscillates, and whether the protective circuit functions etc. If finding

148 Computer Hardware and Architecture

out problems in foresaid aspects, users need to check rectifier diodes, smoothing

capacitors, and three-way regulation tubes at output sides. If power supply stops after

starting up, users shall check whether the power supply remains in protective status by

measuring protective voltage of PWM chip. If the voltage exceeds the specified value,

which means the power supply is in protective status and users shall find out reasons

for the protective status.

8.3 Troubleshooting Input Devices

PS/2 keyboard and mouse not working

See that the device is plugged in the correct port. If the port and cable are color-coded,

the keyboard cable should go into the purple-colored port and the mouse into the green-

colored port. Color coding can vary. Try to switch them up and see if doing so helps

fix the problem. Follow the same process if the PS/2 connectors are identical in color

and you need to identify which one is designated for the keyboard and the mouse.

If the cables are on the right parts and the peripherals still don’t work, try to use other

devices. The keyboard or mouse may need replacement. Blocked keys or sensors. Dirt

blocking the keys or sensors prevents PC peripherals from responding to commands.

Regardless of how much you click on a mouse or press a key, nothing will happen if

contact is not established.

Input devices stop working after updates

Following an operating system or software update, one or two of your attached PC

referrals may no longer work. There are several ways to restore a device’s

functionality.

 Switch USB ports

Doing so will force your computer to recognize a device. A computer system usually

recognizes a device based on their location or the specific USB port where the device

was attached before any updates were made. If the system thinks nothing has changed,

it will not reload drivers, resulting in peripherals not working. Thus, the need to switch

USB ports.

 Start in safe mode

In some cases, a driver in the cache will not load properly after an update. The result

Computer Hardware and Architecture 149

is a broken mouse and keyboard ... or so it might appear. With a bit of a system purge

in safe mode, the boot will reload drivers and load them properly.

 Reset the PRAM

During a firmware update, the PRAM settings of your computer, which include

peripheral devices, video settings, startup disk, and audio volumes, may be

reconfigured. Reset the PRAM to fix the problem. Reboot the system and then press

and hold down the option-command-P-R keys at the same time. Wait for your

computer to reset and chime a couple of times at reboot before you release the keys.

 Power cycle the entire system

Faulty settings may occur after an update. Remove a peripheral device from your

computer and leave it off for a few minutes. For better results, shut down your

computer as well and power cycle it. After 5 to 10 minutes, turn the computer back on

and then plug the attached peripherals back in.

Mouse and keyboard stopped working when the printer is turned on

 Ensure efficient power

This could happen when the USB ports for the keyboard and mouse receive too little

power to work because the printer is hogging all of it. Make sure not to connect the

printer to a USB hub that is shared by the keyboard and mouse. .Another solution is to

plug the devices into different USB ports. Attached peripherals can go at the back of

the computer while the printer is plugged in at the front.

 Fix interference

Do your keyboard, mouse, and printer all use a wireless connection? They could be

interfering with one another, even if one is using radio frequency while the other relies

on Bluetooth. To avoid conflict and establish different frequencies for different

devices, switch off the keyboard and mouse. When you switch them back on, they will

be forced to reconnect to your computer using a free frequency.

 Check driver compatibility

Conflicts between drivers could cause problems with different devices.

Communication with your operating system will be effected and will result in devices

not working properly. Open Device Manager and check that drivers for peripherals

150 Computer Hardware and Architecture

and the printers are updated. Double click on a device and open the Properties

windows. Under Driver tab, check if the option to Update Driver is available. This

means a newer version of a driver is available.

 Reinstall devices

If you’ve done all the steps above and the problem persists, you may need to reinstall

devices to resolve the issue.

1. Remove the PC-attached peripherals from Device Manager.

2. Any related software must be uninstalled from your computer.

3. Restart the system.

4. Switch on the printer and see that it is connected to your computer and working

properly.

5. Reconnect the keyboard and mouse like you’re using them for the first time. This

reinstalls the peripherals and ensures there are no conflicts.

6. Installing, Repairing and Upgrading Operating System

7. PC Maintenance and Troubleshooting Strategies

8. Maintaining and Optimizing Operating System Performance

9. Troubleshooting Operating System and Applications Startup Problems 8.8

Troubleshooting Hardware Problems

10. Connecting to and Setting up a Network using Operating System

11. Operating System Resources on a Network and Security Strategies

12. Supporting Printers

13. Video Display Problems (Video Modes, Resolution, Color, Size)

14. Virus Detection and Protection (Background of viruses, Virus scanning and

Antivirus software)

15. Disaster Recovery (Risk of data, Backup methods devices and media, Backup

scheduling, Recovery of data)

8.4 Installing, Repairing and Upgrading OperatingSystem

This will teach how to install Windows 10 on your PC. To do this, you'll need to hold

down a key while Windows is starting up, which will launch a menu that lets you start

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the computer from either a USB drive or a CD/DVD with the Windows 10 installer on

it. The following instructions show doing a clean install, no programs or data will be

kept. If your desire is to do an update install (Only from Windows 7, 8, or 8.1), when

you follow the instructions below regarding the Windows 10 installation tool, you will

be starting the update while already running your Windows. Any programs not

supported by Windows 10 may be left out, otherwise the programs will be there, and

all your files will remain.

Booting to the Windows 10 Installer

1. Make sure your Windows 10 installation media is connected. In order for you

to install Windows 10, your Windows 10 installation file must be loaded onto a

disc or flash drive, and the disc or flash drive must be inserted into your

computer.

 If you haven't yet downloaded the Windows 10 installation tool, follow the

instructions from this Microsoft support page: https://www.microsoft.com/en-

us/software-download/windows10

2. Open the Start menu. Either click the Windows icon in the bottom-left corner

of the screen, or press the ⊞ Win key.

3. Click the power icon. This is the circle with a line through its top that's in the

bottom-left corner of the Start window.

4. Click Restart. It's in the pop-up menu above the power icon. Doing so will

restart your computer.

5. Press and hold Del or F2 to enter setup. This key may also be a different

key—most computers will display a message on startup that says "Press [key] to

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enter setup" or something similar, so look for this message when your computer

restarts to confirm the key you should press to access the BIOS.

 Consult your computer's manual or online support page to confirm your

computer's BIOS key.

6. Navigate to the Boot tab. You'll use the arrow keys to select it.

 The Boot tab may instead say Boot Options, depending on your

computer's manufacturer.

7. Select a device from which to boot. You have a couple of options here:

 For a USB flash drive, select the Removable Devices option.

 For a disc installation, select the CD-ROM Drive option.

8. Press the + key until your boot option is first. Once either Removable

Devices or CD-ROM Drive is at the top of the list, your computer will select

your choice as its default boot option.

 On some computers, you'll instead press one of the function keys (e.g., F5)

to navigate an option up to the top of the menu. The key will be listed on

the right side of the screen.

9. Save your settings. You should see a key prompt (e.g., F10) at the bottom of the

screen that correlates to "Save and Exit"; pressing it should save your settings

and restart your computer.

 You may have to press ↵ Enter to confirm the changes.

10. Wait for your computer to restart. Once your computer finishes restarting, you'll

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see a window here with your geographical data. You're now ready to begin

setting up your Windows 10 installation.

1. Click Next when prompted. You can also change the options on this page (e.g.,

the setup language) before continuing if need be.

2. Click Install Now. It's in the middle of the window.

3. Enter your Windows 10 key, then click Next. If you don't have a Windows 10

key, instead click Skip in the bottom-right corner of the screen.

4. Click the "Accept" box and click Next. This will indicate that you accept the

5. Click Upgrade. It's at the top of the "Which type of installation do you want?"

window. This option installs Windows 10 while preserving your files, apps, and

settings.

 You can click Custom instead to clean install Windows 10 on your

computer. Doing so will prompt you to select a partition to format before

continuing.

6. Wait for Windows 10 to install. This process may take anywhere from half an

hour to several hours, depending on your computer's previous operating system

and processing speed.

 If prompted to press a key in order to boot from a CD, do not press a key.

7. Follow the on-screen setup instructions. Once Windows 10 has been installed on

your computer, you'll be able to customize its settings (e.g., your region, your

preferred language, location settings, etc.). Once you finish this process, you will

be taken to your computer's desktop.

 You can also click Express Settings to set up Windows 10 with the

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recommended settings.

8. Press the + key until your boot option is first. Once either Removable

Devices or CD-ROM Drive is at the top of the list, your computer will select

your choice as its default boot option.

 On some computers, you'll instead press one of the function keys (e.g., F5)

to navigate an option up to the top of the menu. The key will be listed on

the right side of the screen.

9. Save your settings. You should see a key prompt (e.g., F10) at the bottom of the

screen that correlates to "Save and Exit"; pressing it should save your settings

and restart your computer.

 You may have to press ↵ Enter to confirm the changes.

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10. Wait for your computer to restart. Once your computer finishes restarting, you'll

see a window here with your geographical data. You're now ready to begin

setting up your Windows 10 installation.

1. Click Next when prompted. You can also change the options on this page (e.g.,

the setup language) before continuing if need be.

2. Click Install Now. It's in the middle of the window.

3. Enter your Windows 10 key, then click Next. If you don't have a Windows 10

key, instead click Skip in the bottom-right corner of the screen.

156 Computer Hardware and Architecture

4. Click the "Accept" box and click Next. This will indicate that you accept the

5. Click Upgrade. It's at the top of the "Which type of installation do you want?"

window. This option installs Windows 10 while preserving your files, apps, and

settings.

 You can click Custom instead to clean install Windows 10 on your computer.

Doing so will prompt you to select a partition to format before continuing.

6. Wait for Windows 10 to install. This process may take anywhere from half an

hour to several hours, depending on your computer's previous operating system

and processing speed.

 If prompted to press a key in order to boot from a CD, do not press a key.

7. Follow the on-screen setup instructions. Once Windows 10 has been installed

on your computer, you'll be able to customize its settings (e.g., your region, your

preferred language, location settings, etc.). Once you finish this process, you will

be taken to your computer's desktop.

 You can also click Express Settings to set up Windows 10 with the

recommended settings.

8.14 Disaster Recovery

Disaster recovery (DR) is an area of security planning that aims to protect an

organization from the effects of significant negative events. Having a disaster recovery

strategy in place enables an organization to maintain or quickly resume mission-

critical functions following a disruption. he goal of DR is for a business to continue

operating as close to normal as possible. The disaster recovery process includes

planning and testing and might involve a separate physical backup site for restoring

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operations. An emergency communication plan is another part of a disaster recovery

strategy, enabling an organization to contact staff and relevant emergency response

personnel and keep them updated.

Data risk

Data risk is the protential for a business loss related to the governance, management

and security of data. The following are illustrative examples.

Vendor Lock-in

In a dispute with a software-as-a-service vendor they hold your data as a bargaining

chip and prevent you from accessing it.

Data Loss

A data storage device fails resulting in the loss of transactional data.

Data Corruption

Data becomes corrupted due to data rot causing business processes to fail.

Data Integration

An integration process fails. As a result, customers can't view their most recent

transactions on your website resulting in a flood of complaints.

Dark Data

A firm recklessly accumulates dark data that becomes disorganized and costly to

manage.

Data Availability

A market data feed goes down in the middle of market hours causing disruptions of

trading operations at a bank.

Backup Method and devices and Media

There are many ways to back up your data, from using an external drive to backing up

those files on a remote server over the Internet. Here are the strengths and weaknesses

of each:

 Back Up to an External Drive: If you have an external USB hard drive, you can

just back up to that drive using your computer’s built-in backup features. On

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Windows 10 and 8, use File History. On Windows 7, use Windows Backup. On

Macs, use Time Machine. Occasionally connect the drive to the computer and

use the backup tool, or leave it plugged in whenever your home and it’ll back up

automatically. Pros: Backing up is cheap and fast. Cons: If your house gets

robbed or catches on fire, your backup can be lost along with your computer,

which is very bad.

 Back Up Over the Internet: If you want to ensure your files stay safe, you can

back them up to the internet with a service like Backblaze. Backblaze is the well-

known online backup service we like and recommend since CrashPlan no longer

serves home users (although you could pay for a CrashPlan small business

account instead.) There are also competitors like Carbonite—we also used to

mention MozyHome, but it’s now a part of Carbonite. For a low monthly fee

(about $5 a month), these programs run in the background on your PC or Mac,

automatically backing up your files to the service’s web storage. If you ever lose

those files and need them again, you can restore them. Pros: Online backup

protects you against any type of data loss–hard drive failure, theft, natural

disasters, and everything in between. Cons: These services usually cost money

(see the next section for more details), and the initial backup can take much

longer than it would on an external drive–especially if you have a lot of files.

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 Use a Cloud Storage Service: Backup purists will say this isn’t technically a

backup method, but for most people, it serves a similar enough purpose. Rather

than just storing your files on your computer’s hard drive, you can store them on

a service like Dropbox, Google Drive, Microsoft OneDrive, or a similar cloud

storage service. They’ll then automatically sync to your online account and to

your other PCs. If your hard drive dies, you’ll still have the copies of the files

stored online and on your other computers. Pros: This method is easy, fast, and

in many cases, free, and since it’s online, it protects you against all types of data

loss. Cons: Most cloud services only offer a few gigabytes of space for free, so

this only works if you have a small number of files you want to back up, or if

you’re willing to pay for extra storage. Depending on the files you want to back

up, this method can either be simpler or more complicated than a straight-up

backup program.

While backup programs like Backblaze and cloud storage services like Dropbox are

both online backups, they work in fundamentally different ways. Dropbox is designed

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to sync your files between PCs, while Backblaze and similar services are designed to

backup large amounts of files. Backblaze will keep multiple copies of different

versions of your files, so you can restore the file exactly as it was from many points in

its history. And, while services like Dropbox are free for small amounts of space,

Backblaze’s low price is for as big a backup as you want. Depending on how much

data you have, one could be cheaper than the other.

Backblaze and Carbonite do have one big limitation you should keep in mind. If you

delete a file on your computer, it will be deleted from your online backups after 30

days. You can’t go back and recover a deleted file or the previous version of a file after

this 30 day period. So be careful when deleting those files if you might want them

back!

Backup scheduling

Backup scheduling is one of the most important features in data backup software.

It allows completely eliminating manual backups (with all filtering, compressing,

transferring to the storage, and other).

A good backup system will have a schedule that allows you to easily verify that all of

the required information is being backed up on a regular basis. This means rotating

your tapes or video information as well as backing up your files within your office. If

you schedule a nightly or weekly backup, you can limit the amount of data that is lost

in the event that a computer or your entire system were to fail.

A scheduled backup allows you to relax because you know that all of your information

is being backed up, and you are limiting what you may lose. In years past this meant

making a physical copy of the files and then shipping them to another location. Often

businesses would use microfiche to cut back on storage space.

Using Automatic Backups

An automatic backup will make backing up your information much easier. It

eliminates human error. You can schedule automatic backups of the data on your

company’s computers. This can be done with both an external hard drive and an offsite

server. These automatic backups will run in the background while your employees are

working, and should not negatively impact your workflow. Automatic backups

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simplify the entire backup process.

Choosing Where to Backup

Once you have established scheduled backup system, you will need to choose where

to store your data. Many companies prefer a redundant backup system. This means

that you store the information offsite in one or two additional locations. Cloud

computing is one way of doing this. If you are worried about the data you are storing,

you can use an offsite server to store your information.

Data recovery

It is the process of retrieving or restoring digital information that is no longer

accessible for some reason. A good example would be any file that was

mistakenly deleted, lost, or corrupted. The data recovery process varies based on the

circumstances under which it was lost.

Process of Data recovery

One solution is third-party software. Many software utilities can recover lost data. One

can pay certain money for data recovery, depending on their capabilities. There are

also companies that will perform data recovery for a range of fees. They specialize in

difficult cases where a software utility was not successful and part replacement is

necessary. An example is a hard drive that was in a fire and needs its disk interface

board replaced before data can be recovered. Below is a listing for a few of the major

data recovery companies.

 Action Front Data Recovery

 CBL Data Recovery Technologies nc.

 Doctor Byte

 DriveSavers Data Recovery

 Kroll Ontrack

 Lazarus Data Recovery

 Secure Data Recovery Services

 Stellar Data Recovery

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