Info Tech - Chapter 1

7/31/2019 Info Tech - Chapter 1

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CA-IPCC-Information TechnologyCHAPTER 1: Information Technology

Study Tips and Examination Technique

Know Your Syllabus

Go through the syllabus carefully The study material is divided into chapters based on the syllabus.

Plan Your Study

Make a study plan covering the entire syllabus and then decide how much time you can allocate to

the subject on daily/weekly basis.

Maintain the time balance amongst various subjects such as purely descriptive type and numerical-

based papers.

Always assess your preparation periodically, say, on weekly basis. If necessary, revise your plan and

allocate more time for the subjects in which you feel deficient.

Prepare Study Strategy

Read, understand and assimilate each chapter.

First of all, have an overview of the chapter to understand the broad contents and sequence of vari-

ous sub-topics.

Prepare notes in the manner you feel comfortable covering all key points

Always try to attempt the past year examination question papers under examination Conditions

Revision of material should never be selective in any case. Broad coverage of the entire syllabus is

more important than preparing 2-3 chapters exhaustively.

Examination Technique

Reach examination hall well in time.

Plan your time so that equal time is awarded for each mark. Keep sometime for revision as well.

Always attempt to do all questions. Remember that six average answers fetch more marks than

five best answers. Therefore, it is important that you must finish each question within allocated

time.

Read the question carefully more than once before starting the answer to understand very clearly asto what is required by the paper-setter.

Always be concise and write to the point and do not try to fill pages unnecessarily.

In case a question is not clear, you may state your assumptions and then answer the question.

While writing answers in respect of essay-type questions, try to make sub-headings so that it catches

the examiners eye. In case of case-study, be very precise and write your conclusion in a clear man-

ner.

Revise your answers carefully and underline important points before leaving the examination hall.

Wishing you all the Best

9966080268/78 1 Haranathapuram,Nellore-3.


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CA-IPCC-Information Technology

Information Technology (50 Marks)

1) Introduction to Computers

2) Input and Output Devices

3) Computer Software

4) Data Storage, Retrieval and DBMS

5) Computer Networks & Network Security

6) Internet and Other technologies

7) Flow charts

8) Decision Tables

Strategic Management (50 Marks)

1) Business Environment

a) General Environment Demographic, Socio-cultural, Macro-economic, Legal/political

b) Competitive Environment

2) Business Policy and Strategic Management

Meaning and nature; Vision, Mission and Objectives; Strategic levels in organizations.

3) Strategic Analyses

Situational Analysis SWOT Analysis, TOWS Matrix, Portfolio Analysis BCG Matrix.

4) Strategic Planning

Meaning, stages, alternatives, strategy formulation

5) Formulation of Functional Strategy

Marketing Strategy, Financial strategy, Production strategy, Logistics strategy, Human resource

strategy.

6) Strategy Implementation and Control

Organizational Structures; Establishing Strategic business units etc.

7) Reaching Strategy Edge

Business process Reengineering, Benchmarking, TQM, Six Sigma etc.



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Chapter-1

Introduction to Computers

Scope of this chapter: - Generation of Computers and their evolution

Classification of computers.

Features of computers, their advantages and limitations

Basic components of a computer system.

Types of Storage devices, their use and capacity.

Types of RAM and their working.

1.1 Historical Development of Computers

The modern computer with the power and speed of today was not a solitary invention that sprang com-

pleted from the mind of a single individual. It is the end result of countless inventions, ideas, and devel-

opments contributed by many people throughout the last several decades.

1.2 Generation of Computers and their evolution

The modern computer with the power and speed of today was not a solitary invention that sprang com-

pleted from the mind of a single individual. Many people contributed their ideas, inventions and devel-

opments to the present computer what we see.

We can compare the evolution of computer with the Mobiles, initial mobiles use to be big in size and

without no camera and it is used only for the purpose of talking between people, but the latest mobiles

are very sleek in size and with high end technology inbuilt in them like Cameras, Video Recording,

Voice Recognition and Internet etc,.

We shall read about each generation and the developments that led to the current devices that we use to-

day.

First Generation Computers: UNIVAC (Universal Automatic Computer) was the first computer com-

mercially available and marks the beginning of first generation of electrical computers. These computer

systems are made of Vacuum Tubes. The input and output units were the punched card reader and the

card punches.

Below is the picture of Magnetic Drum Memory & UNIVAC Computer


Generation of ComputersGeneration of Computers

First GenerationComputers(1940-1956)

ThirdGenerationComputers(1964-1971)

Fifth GenerationComputers (1990and beyond)

SecondGeneration

Computers(1956-1963)

Fourth Generation

Computers (1972-1990)


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Below is a sample picture of Punched cards

Features:

1. Computers were large in size (25 feet by 50 feet; 5600 tubes)

2. These computers uses vacuum tube for data processing and storage, Cannot be reliedcom-

pletely as the vacuum tubes burned out during operations.

3. Requires Air Conditioningdue to the high level of heat generation.

4. They had a memory size of 20 bytes and speed of 5 mbps

5. They use punch card for data storage.

6. The programmers were machine dependent.7. Lower Internal Storage capacity (Magnetic Drums).

8. High consumption of Electric power.

9. Low speed of processingdue to the low speed of input and output devices (Punched Cards).

10. Use of Low level language (Machine language).



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Second Generation Computers: These computers used Transistors instead of Vacuum tubes. Transis-

tors were invented in 1947 but seen widespread only from 1950s IBM 1401 was the most popular sec-

ond generation computer.

The transistor was far superior to the vacuum tube, allowing computers to become smaller, faster, cheap-

er, more energy-efficient and more reliable than their first-generation predecessors.These were also the first computers that stored their instructions in their memory, which moved from a

magnetic drum to magnetic core technology. The first computers of this generation were developed for

the atomic energy industry.

Features:

1. They were capable of translating, process and store data.

2. They were much smaller in size than first generation computers.

3. They had got memory size of 32 bytes and speed of 10 mbps, high processor speed.

4. Generated low level of heatand required less power.5. Greater degree ofreliability.

6. They use punch card for data storage.

7. Moved from Machine language to Assembly language and also initial high level language like

COBOL and FORTRAN.

Due to use of high level language and high level of operating system the computers were used by variety

of users like by commercial users and scientific users.

Third Generation Computers:

Third Generation computers were built using the new technology called Integrated Circuits (IC).



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CA-IPCC-Information TechnologyThe ICs are silicon chips which are tiny in size; contain thousands of individual components integrated

in a small chip. Thus the computers were compact, faster, more reliable, required less power and low

cost.

These computers can be used for both Scientific and business applications.

Features:1. They were much more powerful and smaller in size than second generation computers.

2. They used integrated circuit (I.C.) to store data which consisted of many transistors, increased pro-

cessing speed.

3. The hardware cost and maintenance cost was much lower than second generation of computer.

4. They weregenerally used for business and scientific purposes

5. They uses storage disk for data storage e.g. magnetic disks, tapes.

6. Third generation computers were more reliable compared to other previous generations.

7. The operating systems were introducedin this era.

8. In this generation, high level programming languages were used. For e.g. Fortran, COBOL, PAS-

CAL and BASIC.

9. Third generation computers permitMulti Programming and Time Sharing.

Fourth Generation computers: Fourth generation machines appeared in 1970s utilizing still newer

technology which enabled to be even smaller and faster than third generation computers.

The IC technology in the third generation was mainly MSI (Medium scale integration), where as the

fourth generation computer adopted the IC technology with LSI (Large Scale Integration) and VLSI

(Very Large scale Integration), further gone for ULSI.

The microprocessor brought the fourth generation of computers, as thousands of integrated circuits were

built onto a single silicon chip that contains a CPU. In the world of personal computers, the terms micro-

processor and CPU are used interchangeably.

Three basic characteristics differentiate microprocessors are:

Instruction Set: The set of instructions that the microprocessor can execute.

Bandwidth: The number of bits processed in a single instruction.

Clock Speed: Given in megahertz (MHz), the clock speed determines how many instructions per

second the processor can execute.

Micro computers are fully assembled computer into single machine, which consisted of Keyboard, pro-

cessor unit, CRT and built in cassette tape recorder.

IBM PC, with the introduction of personal computer by IBM in 1981, and apple introduced the Macin-tosh in 1984, individuals also started buying the computers for their personal uses, thus computers

stepped out of large organisations and entered into homes.



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Features:

1. More compact and smaller in size than the third generation computers.

2. Use of LSI and VLSItechnology of Integrated Circuits.

3. Enhanced capability of input and output devices.

4. Introduction ofMicro Computers and Personal Computers.5. Computers are designed withgraphical user interface which is user friendly.

6. Use ofHard disk as storage device, which are also available in the sizes of 80 GB to 500 GB

and Terra bytes.

7. Technology of NetworksLAN (Local Area Network) and Wan (Wide Area Network) is used

for information accessing and sharing.

8. VeryHigh speed of Microprocessor.

9. Use ofObject oriented programming languages (OOPs)like Java, C++ have made the software

more reliable and efficient.

Fifth Generation Computers: Fifth generation computing devices, based on artificial intelligence, are

still in development, though there are some applications, such as voice recognition, that are being used

today.

Artificial Intelligence is the branch of computer science concerned with making computers behave likehumans. The term was coined in 1956 by John McCarthy. Artificial intelligence includes:

Features:

1. Games Playing: Programming computers to play games like chess and checkers.

2. Expert System: Programming computers to make decisions in the real life situations, (for example,

some expert systems help Doctor to Diagnose the diseases based on symptoms).

3. Natural Languages: Programming computers to understand natural human languages.

4. Neural Network: Systems that simulate the intelligence by attempting to reproduce the types of

physical connections that occur in the brains.5. Robotics: Programming computers to see and hear and react to other sensory stimuli.

Natural-language processing offers the greatest advantage we could simply walk up to a computer and

talk to it. Unfortunately, programming computers to understand natural languages has proved to be more

difficult than originally thought.

There are also voice recognition systems that can convert spoken sounds into written words, but they do

not understand what they are writing; they simply take dictation.

Currently, no computers exhibit full artificial intelligence (that is, are able to simulate human behavior).

The greatest advances have occurred in the field of games playing. The best computer chess programs

are now capable of beating humans. In May, 1997, an IBM supercomputer called Deep Blue defeated

world chess champion Gary Kasparov in a chess match.



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CA-IPCC-Information TechnologyComputers and technology of present may have few features of fifth generation computers like voice

recognition, Expert systems used by Doctors in Diagnoses of patient needs.

1.3 Classification of Computers

Computers are generally classified on the basis of various factors:

1) On the basis of working principals2) On the basis for Size and data processing

1.3.1 On the basis of working Principals

On the basis of working principals of computers, they can be categorized into Analog, Digital and Hy-

brid computers.

a) Analog Computer

An analog computer (spelt analogue in British English) is a form of computer that uses continuous phys-

ical phenomena (occurences) such as electrical, mechanical, or hydraulic quantities to model the prob-

lem being solved. It is different from the digital computer in that it can perform numerous mathematical

operations simultaneously. It is also unique in terms of operation, as it utilizes continuous variables for

the purpose of mathematical computation.

b) Digital Computer

A computer that performs calculations and logical operations with quantities represented as digits,

usually in the binary number system. A digital computer is designed to process data in numerical form;

its circuits perform directly the mathematical operations of addition, subtraction, multiplication, and

division. The numbers operated on by a digital computer are expressed in the binary system; binary dig-

its, or bits, i.e. 0 and 1.

Binary digits are easily expressed in the computer circuitry by the presence (1) orabsence (0) of a cur-

rent or voltage.

A series ofeight consecutive bits is called a byte; the eight-bit byte permits 256 different on-off

combinations.

Each byte can thus represent up to 256 alphanumeric characters, and such an arrangement is called a

single-byte character set (SBCS);

A digital computer can store the results of its calculations for later use, can compare results withother data, and on the basis of such comparisons can change the series of operations it performs.



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CA-IPCC-Information TechnologyDigital computers are used for reservations systems, scientific investigation, data-processing and word-

processing applications, desktop publishing, electronic games, and many other purposes like business

transaction processing etc.

c) Hybrid Computer (Analog + Digital)

A combination of computers those are capable ofinputting and outputting in both digital and analogsignals.

Hybrid computer is a digital computer that accepts analog signals, converts them to digital and pro-

cesses them in digital form. This integration is obtained by digital to analog and analog to digital con-

verter.

A hybrid computer capable of real-time solution has been less expensive than any equivalent digital

computer. Hybrid computers have been necessary for successful system development.

An example of a hybrid computer is the computer used in hospitals to measure the heartbeat of the

patient.

Hybrid Machines are generally used in scientific applications or in controlling industrial processes; they

have only a limited usage not suitable for business applications.

1.3.2 On the basis of size and data processing power

Based on the Processing speed, memory capacity and nos. of users computer can handle simultaneously

the computers can be categorized as below: -

(1) Super Computer:

These are the largest, fastest and most expensive computers available, but are not intended for com-

mercial data processing. They are used to process complex scientific applications such as weather re-

search, defence, air craft design and computer generated movies.

Super computer were introduced in 1960 as the worlds most advanced computer. As of May 2010,

the Cray Jaguar is the fastest supercomputer in the world.

The first super computer was ILLIAC IV made by Burroughs. Other players in the manufacture of

super computer are CRAY, IBM, HITACHI and Sun Microsystems, etc.

The main characteristic that distinguishes the super computer from others is the high degree of paral-

lelism, i.e., their ability to perform large number of operations simultaneously.


Sizes/Categorization of Computers

Mini Com uter PC/ Micro Com-puter

Work Station ServerMainframe Com-Su er Com uter


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CA-IPCC-Information Technology The processing speed of a super computer can range between 10,000 MIPS (Million instructions per

second) to 1.2 BIPS (Billion instructions per second).

In general, the speed of a supercomputer is measured in "FLOPS" (FLoating Point Operations Per

Second).The FLOPS is a measure of a computer's performance, especially in fields of scientific cal-

culations that make heavy use of floating point calculations, similar to the older, simpler, instruc-

tions per second. "Petascale" supercomputers can process one quadrillion (1015

) (1000 trillion)FLOPS.

They can support up to 10,000 terminals at a time.

(2) Main Frame Computer: Main frames are less powerful and cheaper than the super computer but

Faster and costlier when compared with Mini computer.

Mainframe can process at several million instructions per second and can support more than 1,000 re-

mote terminals.

Prices of Mainframe computer will range between 1 Crore to 5 Crores depending on the configurations.

Major suppliers of Mainframe computers are IBM, Honey Well, etc.

Mainframe normally used as central computer of big organizations like stock exchange, Banks Head of-

fices (for Core banking) etc.

Mainframes are also used for applications like Railway reservation or Airline reservation systems.

(3) Mini Computer: Minicomputer performs data processing activities in the way as the mainframe but

on a smaller scale.

Minicomputer is small compared with a mainframe and can be called as scaled-down mainframe, also

called as multi user computer as many persons can connect to the same CPU.

Cost of minicomputer will range from Rs. 5 lacs to Rs. 50 lacs. Most popular mini computer manufac-

turers are IBM; DEC etc.



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CA-IPCC-Information TechnologyProgramming languages used by minicomputer include BASIC, PASCAL, COBOL, C and FOR-

TRAN.

Minicomputer systems can be equipped with most of the input/output (I/O) devices and secondary stor-

age devices that the large mainframe systems can handle, such as terminals and Hard Disks. They are

also making possible the installation of distributed data processing systems. Instead of a company hav-ing one large mainframe computer, it may have minicomputer at each of its remote locations and con-

nect them to each other through telecommunications.

(4)Microcomputers: A Microcomputer is a full-fledged computer system that uses a microprocessor as

its CPU; these are also called personal computer systems.

Microprocessor is a small silicon chip which consists of several integrated circuits used for processing.

Once this microprocessor is combined with other chips like input, output and memory chips on the

mother board then it will take the form of microcomputer.

IBM and Apple are the two most popular players in the microcomputer manufacturing.

The computers that we see in houses, offices are examples of Microcomputers.

Microcomputer in the markets normally contains the below listed: -

CPU : Centrino Duo, Pentium IV, Core 2 Duo, i3, i5, i7

Mother Board : Intel865

Primary Memory (RAM) : 2 GB to 8 GB, DDR3

Secondary Storage : Hard Disk 250 GB or 500 GB, DVD Writer (Blu Ray Combo).

Output Devices : 17 CRT or LCD Monitor, Laser/Jet PrintersInput Devices : Keyboard, Mouse, and Scanner etc.

Processor : 16, 32 or 64 bit processor.

(5) Work Stations: Workstation is a high-end microcomputer designed for technical or scientific

applications.

Workstation just looks like a personal computer and is typically used by one person, they are commonly

connected to a local area network and run multi-user operating systems.

The term workstation has also been used to refer to a mainframe computer terminal or a PC connected to

a network.

Workstation significantly differs in two areas from microcomputers:Workstations are constructed on different architecture of CPU called RISC(Reduced Instruction Set

Computing) due to which processing of instructions will be faster than microcomputers.



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CA-IPCC-Information TechnologyWorkstation typically runs on UNIXOS whereas the microcomputer can be run on DOS, UNIX, OS/2

and Windows.

The most prominent manufacturers of Workstation are Sun Microsystems. Other Manufacturers include

DELL, DEC(Digital Equipment Corporation), IBM, HP.

6) Server: A Server is a computer system that provides services to other computing systems calledclients over a network.

The typical server is a computer system that operates continuously on a network and waits for requests

for services from other computers on the network.

Many servers are dedicated to this role, but some may also be used simultaneously for other purposes,

particularly when the demands placed upon them.

For example, in a small office, a large desktop computer may act as both a desktop workstation for one

person in the office and as a server for all the other computers in the office.

However, servers run software that is often very different from that used on desktop computers and

workstations. Servers primarily use some hardware and software to provide shareable services, example

Web Server; Printer Server; Mail Server etc.

1.4 Advantages and Limitations of Computers:

The Computers are very vastly used in present days, by the use of technology of computers the infra-

structure and communication became fast. Life became difficult without computers and technology. Be-

low are some advantages of computer:

1. Speed: The computers carry out the operations at a very high speed which cannot be imagined or

viewed by the human beings. The smallest unit of time in the human experience is Second, but when it

comes to the computers the operations are measured in milliseconds (10-3 Seconds), microseconds (10-6

Seconds), nanoseconds (10-9 Seconds) and picoseconds (10-12 Seconds).

The computer generates signals during the operation process therefore the speed of computer is usually

measure in megahertz (MHz) or gega hertz (GHz). It means million cycles units of frequency per sec-

ond. Different computers have different speed.

2. Accuracy & Precision: Accuracy is an issue pertaining to the quality of data and number of errors

contained in the data set.The accuracy is important to rely and act upon on any information; computers

even processing at high speed will deliver the results with accuracy. Level of accuracy required varies

from application to application basing on the rounding of fraction values.



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CA-IPCC-Information TechnologyExample - commercial data processing accuracy of the values can be up to 2 to 4 decimal points, in case

of scientific applications the accuracy of the value may be required up to 12 to 15 or even more decimal

points.

3. Reliability:Now a days the computers down time came down drastically, their up time can be said at

99% i.e. computer has almost nil down time. Down time means the time during which computers are notavailable for processing. Even in case of disasters or emergency system crashes many plans are in place

to run the systems from the backup systems which may be located at different place.

The IEEE defines it as "the ability of a system or component to perform its required functions un-

der stated conditions for a specified period of time."

4. Memory Capability/Storage: The data which is processed for the commercial purpose or any scien-

tific purpose needs to be stored and should be able to access or retrieve when ever required with less ef-

fort. Thus Memory is more important, Computer systems have total and instant recall of data and an al-

most unlimited capacity to store these data.

5. Communication: With the advanced technology in the networking the computers will be able to

transfer the information from one place to another immediately. Example When we send a mail, it

reaches to the destination in few seconds.

Computers in the combination of the networks made possible of business style Any Time Any

Where eg- ATM Machines, where we can draw cash, check balance etc.

6. Automation: A computer can automatically perform operations without interfering with the user dur-

ing the operations. It controls automatically different devices attached with the computer. It executes au-

tomatically the program instructions one by one.

7. Versatility: Versatile means flexible. Modern computer can perform different kind of tasks done by

one or simultaneously. It is the most important feature of computer. At one moment we can play games

on computer, the next moment we can compose and send emails etc. In colleges and universities com-

puters are used to deliver lectures to the students. The talent of computer is dependent on the software.

8. Consistency: People often have difficulty to repeat their instructions again and again. For example, a

lecturer feels difficulty to repeat a same lecture in a class room again and again. Computer can repeat ac-

tions consistently (again and again) without loosing its concentration. A computer will carry out the ac-

tivity with the same way every time.

Limitations: Despite of all the above advantages computers also has their own limitations or disadvan-

tages as listed below -

1. Programming: Any computer to perform it requires instructions for what to do, how to do and when

to do. These instructions for a computer can be called as programmes.

Thus if the program is correct with no errors then the actions performed by the computer will be accurate

and reliable.

2. No Intelligence: Although computers are faster, more diligent, accurate and versatile than human be-

ings, it cannot replace them. Unlike human beings, computers do not have any intelligence. Its perfor-mance is depends on instructions given to it. It cannot carry any task at its own.



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CA-IPCC-Information Technology3. No decision making power : Computer cannot make any decisions nor can it render any help to

solve a problem at its own like that if we plays chess with computer, the computer can take only those

steps which is entered by the programmer. It cannot move at its own.

4. Curtail human Capabilities: Although computers are great help to human beings. It is commonly

felt that we people have become so dependent on calculator that we cannot make very simple calculationwithout calculator. Sometimes, find it difficult to instantly speak out even those telephone numbers

which they use every now and then as they have got the habit of using them by retrieving the storage.

Further, excessive use of computers is causing various type of health injuries such as cervical and back

pain, pain in eye, headache.

5. Application logic must be understood: computer may not be helpful to people in areas where sub-

jective evaluations are important. For example, it may not be able to tell a sales manager if a new prod-

uct will be successful. But the computer can tell the manager how the product will fare under assumed

price, cost, and sales volume conditions. These assumed values could be fed into the computer.

6. Data input: The computers will perform all the operation using the programs on the data input; when

the data is not reliable and accurate even though the program is correct the out put will be wrong. In

computer terms it is popularly known as GIGO (Garbage In and Garbage Out). The output of the pro-

grams will be based on the input data and the accuracy of the programs.

7. Skilled Manpower: The availability of the skilled manpower is also one limitation, now days the

availability is increasing.

Conclusion: - Despite of the above few limitations the computers have become very popular and been

part of human life, where it is very difficult to imagine the life without computer.

1.5 Basic Computer Architecture

1.5.1 Basic computer functions

In Computer System, different parts of a computer are organized in such a way that, it helps to per-

form various operations to complete the given specific task. Widely computers are used to perform

arithmetic calculations. However, now-a-days computer is used for many other purposes. A comput-

er as shown in figure performs basically five major operations or functions irrespective of their size

and make. These are

1. It accepts data or instructions by way of input,

2. It stores data,

3. It can process data as required by the user,

4. It gives results in the form of output, and

5. It controls all operations inside a computer



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1. Input: It is the process of entering data and programs into the computer system. Input is further pro-

cessed to produce the required results. Input will be received in a prescribed format.

2. Storage: The process of saving data and instructions permanently is known as storage. The primary

storage of the computer system is designed to supply data and inputs to CPU so to meet its speed of

processing, the storage is not permanent. The Secondary storage is used to store the data permanent-

ly. The storage unit performs the following major functions: All data and instructions are stored here before and after processing.

Intermediate results of processing are also stored here.

3. Processing: The task of performing operations like arithmetic and logical operations is called pro-

cessing. The Central Processing Unit (CPU) takes data and instructions from the storage unit and

makes all calculations based on the instructions given and it is then sent back to the storage unit.

4. Output: This is the process of producing results from the computer to users. The output produced by

the computer can also be kept inside the computer for further usage or can be directly sent out.

5. Control: The manner how instructions are executed and the above operations are performed. Con-

trolling of all operations like input, processing and output are performed by control unit. It takes care

of step by step processing of all operations inside the computer.

1.5.2 Component of Computer Systems CPU

Computer needs two things to function properly, Hardware and Software.



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CA-IPCC-Information TechnologyHardware consists of several physical components like Key Board, CPU, Monitors, Mouse and other

peripheral devices CD/DVD Drive, modems, Printers etc.

Software consists of programs which are further classified as System programs (e.g. Operating System

like Windows, DOS) Application programs (MS-Word, MS-Excel, Tally etc.)

Computer Hardware is classified as CPU and Peripheral Devices.1.5.2.1 Central Processing Unit (CPU):

The Central Processing Unit (CPU).also known as the processor is the heart, soul and brain of the com-

puter. In a microcomputer, the entire CPU is contained on a tiny chip called a microprocessor

Currently the Pentium chip or processor, made by Intel, is the most common CPU, this is the most im-

portant part on the mother board (a platform which allows all the devices stay connected and flow of

data among them).

Every CPU has at least two basic parts, Control Unit and Arithmetic Logical Unit which co ordinates

with each other.

1. Control Unit:

All the computers resources are managed from the control unit. The Control unit function is to co ordi-

nate all the activities of the computer like controlling the inputs and outputs.

Any instruction which involves movement of data from one device to another like from primary memory

to printer or Storage device (Hard Disk) etc is executed by control unit and if any instruction contains

arithmetic and logical operation on data then it is transferred to ALU.

A CPU contains in built instructions for carrying out various types of operation. Each instruction or in-

struction set is expressed in microcode-a series of basic directions that tell the ALU how to execute.

To execute any instruction, the instruction is first of all reaches to Control unit, which created the corre-

sponding microcode and passes it to ALU, where the actual execution of the instruction takes place.

Usually, when a new CPU is developed, the instruction set has all the same commands as its predecessor

plus some new ones. Therefore, more the instructions in the instruction set of CPU more advance is the

CPU.



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2. Arithmetic Logic Unit: As said earlier every instruction to the computer first reaches the control unit

and if it contains any Arithmetic or Logic operation the respective microcode is passed to the ALU (Sec-

ond component of CPU).

ALU includes a group of circuits and registers, Circuits to process data and registers which are high

speed storage used to hold the data currently being processed, (this is a temporary memory).

ALU can perform two types of operations, Arithmetic operations like addition, subtraction, multiplica-

tions and divisions. Logical operations like comparison between two numbers or text.

1.5.2.2 Various features of Central Processing Unit (CPU): Over a period of time, the processor has

evolved from slow 286s or 386s running at speeds as low as 20 MHz to present day Pentium III and IV

running at a whooping 3 GHz (3000 MHz i.e. 3,000,000,000 cycles) Now we take a closer look at the

various features that the Central Processing Unit of a PC offers.


Important Features of CPUImportant Features of CPU


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Lets have a look at the picture of CPU cabinet

1. Clock Speed: The clock speed is the speed at which the processor executes instructions. Clock speed

is measured in megahertz (MHz).which is a million cycles per second, therefore processor Pentium IV

with 3 GHz (3000 MHz) executes 3000 million instructions per second.

Higher the clocks speed, the faster the processor, the better the system performance. Also, some micro-processors are super scalar, which means that they can execute more than one instruction per clock cy-

cle.

2. Cache Memory: Processors incorporate their own internal cache memory. The cache acts as tempo-

rary memory and boosts processing power significantly. The cache that comes with the processor is

called Level One (L1) cache. This cache runs at the processors clock speeds, and therefore is very fast.

The L1 cache is divided into 2 sections. One for data, the other for instructions. Generally, more the L1

cache, faster the processor.

Additionally, PCs also include a much slower secondary, or Level Two (L2) cache. This cache resides

on the motherboard and delivers slower performance when compared with the L1 cache. To overcome

this limitation, newer chips (Pentium II and Pentium III) house the L2 cache in a cartridge along with the

CPU.

Working of Cache Memory:

It is a memory of main processor. Whatever data we send to computer first of all it reaches to main

memory (RAM). From this main memory it goes to processor (CPU) for processing and it comes to

main memory once processing is finished.

As the processor is much faster than the main memory, lot of time is consumed in transferring the databack and forth between main memory and processor.


Cache

Memory:

Internal

Memory of

CPU

CPUs Slot &

Socket:

Holder ofCPU on

Mother Board

MMX (Multimedia

Extension):

Instruction set in

CPU which process

Audio & Video data

Density:

No. OfTransistors in

CPU

Clock Speed:

Measurementof Instructionprocessing

speed of CPU


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CA-IPCC-Information TechnologyIn order to reduce the time consumed in transferring of data between main memory and Processor, we

use cache memory which is inside the processor itself and much faster than RAM.

As shown in the memory diagram with cache memory the CPU will be communicating with high speed

cache memory in place of normal RAM therefore, the effective processing speed of computer would in-

crease.

3. Slot: A CPU socket or CPU slot is an electrical component that is attached to a printed circuit board

(PCB) and is designed to house a microprocessor. It is a special type of integrated circuit socket de-

signed for very high pin counts.

A CPU socket provides many functions, including providing a physical structure to support the CPU,

providing support for a heat sink, facilitating replacement (as well as reducing cost) and most important-

ly forming an electrical interface both with the CPU and the PCB.

Different processors use different sockets or slots to fit onto the motherboard. Based on the type of pro-

cessors, there are various types of slots.



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4. Density: A CPU is made up of millions of small transistors. A CPU performs all the calculation and

manipulation operations by synchronising between the transistors. Therefore, the shorter the distance be-

tween two transistors on a CPU, the faster the performance. Older CPUs had a distance of one micron

between the transistors. But, newer CPUs have a distance as small as 0.35 micron between two transis-

tors, delivering faster performance.

5. MMX: MMX stands for Multimedia extensions a set of instructions built into the CPU, specifically

intended for improving the performance of multimedia or graphic applications like Games, Videos and

Audio applications.

The processors which have the inbuilt instructions for multimedia data processing are called as proces-

sors with MMX features. MMX is now normal or default feature of all the CPU.

1.6 Components of Mother Board: The motherboard or the system board is the main circuit board on

the computer. It acts as a direct channel for the various components to interact and communicate with

each other. There are various types of motherboards available (depending on the processors that are

used)

Above is a snapshot of mother board and its components

Following are the main components of mother board:



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CA-IPCC-Information Technology1.6.1 Processor slot: The processor slot houses the processor. It is rectangular connector into which the

processor is mounted vertically. It also refers more specifically to a square-shaped connector with many

small connectors into which the processor is directly inserted.

1. BIOS: BIOS stands for Basic Input Output System, a small chip on the motherboard that loads the

hardware settings required to load various devices like keyboards, monitors, or disk drives. BIOS is also

known as ROM BIOS because it is ROM chip (IC) which contain system software known as Basic in-

put output system which used for initial operation of computer.

BIOS contain permanent instructions or programs also known as start up programs used in booting or

starting of computer.

2. CMOS (Complimentary Metal Oxide Semiconductor): The PC uses the CMOS memory to store

the date, time and system setup parameters.

These parameters are loaded every time the computer is started. A small Lithium Ion battery located on

the motherboard powers the CMOS as well as the BIOS.

3. Power supply connectors: The power supply connectors allow the user to connect the power supply

unit to the motherboard and provide power for the functioning of the various devices or components

like CD/DVD writer, Hard Disk, etc.

16.2 Expansion Slots and Boards: PCs are designed so that users can adapt, or configure the machines

to their own particular needs. PC motherboards have two or more expansion slots. These slots are used

normally for I/O devices like graphical adopter card on which the visual display unit is attached. Simi-

larly we can put the Modem card to use the internal modem. These expansion slots are also used for con-

necting CD/DVD drive, external Hard disk or Pen drives etc.



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CA-IPCC-Information TechnologyIn general these are known as expansion slots as these slots helps to expand the capability of the com-

puter by attaching more devices or using computer with added capability like TV tuner card is used in

expansion slot to use the computer as TV.

Picture of Expansion Slots

Some of the Slots are briefly discussed below:

1. SIMM/DIMM slots: SIMM stands for Single Inline Memory Modules, while DIMM stands forDual Inline Memory Module. SIMM/DIMM slots are used to house RAM modules. Now a day almost

all the computers are using DIMM as the SIMM is outdated technology.

2. PCI slots:Now a day almost all the expansion slots provided on mother board are of PCI types. The

PCI (Peripheral Component Interface) slots are used for connecting PCI-based devices like graphics ac-

celerator cards, sound cards, internal modems or SCSI cards.

3. AGP slot: All Celeron and Pentium-III/P-IV motherboards come with an AGP (Accelerated Graph-

ics Port) slot. AGP is a dedicated slot meant to provide faster access to AGP-based graphic accelerator

cards, thus enhancing the visual experience for the user. AGP card normally keeps a dedicated proces-

sor for graphic processing and video RAM for storing graphical data for a quality output of graphical

data.

4. ISA: Industry Standard Architecture was a computer bus standard for IBM compatible computers.

This is most ancient type of expansion slot ever used in the computer system. The ISA enables con-

trollers connect directly to the bus to communicate directly with the other peripherals without going

through the processor. However, the ISA bus only allows hardware to address the first 16 megabytes of

RAM.

5. SCSI: It is a device interface that is used to solve the problem of a finite and possibly insufficient

number of expansion slots. It is calledsmall computer system interface (SCSI pronounced .scuzzy.) In-



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CA-IPCC-Information Technologystead of plugging interface cards into the computers bus via the expansion slots, SCSI can be inserted in

one expansion slot and we can extend that slot to outside the computer by way of a cable. In other

words, SCSI is like an extension cord for computer bus. The current standard is SCSI - 3, which allows

upto 7 devices to be chained on a single SCSI port. Now-a-days many devices support the SCSI inter-

face. Fast, high-speed hard disk drives often have SCSI interfaces, so do scanners, tape drives and opti-

cal storage devices.

1.6.3 Cards:Cards are components added to computers to increase their capability or to have additional functionali-

ties. When adding a peripheral device one should ensure that the computer has a suitable slot.

Sound cards allow computers to produce sound like music and voice. The older sound cards were 8 bit

then 16 bit then 32 bit.

Colour cards allow computers to produce colour. The first colour cards were 2 bit which produced 4

colours [CGA]. Next came 4 bit allowing for 16 [EGA and VGA ] colours Then came 16 bit allowing

for 1064 colours and then 24 bit which allows for almost 17 million colours and now 32 bit is standard

allowing monitors to display almost a billion separate colours.

Video cards allow computers to display video and animation. Some video cards allow computers to dis-

play television as well as capture frames from video. A video card with a digital video camera allows

computer users to produce live video (Web Cam). A high speed or network connection is needed for ef-

fective video transmission.

Many video cards offer added functions, such as accelerated rendering of 3D scenes and 2D graphics,

video capture, TV tuner adapter, MPEG-2/MPEG-4 decoding,

Network cards allow computers to connect together to communicate with each other. Network cards

have connections for cable, thin wire or wireless networks.

http://en.wikipedia.org/wiki/File:SCSI_25-50.jpghttp://en.wikipedia.org/wiki/File:Scsi-1_gehaeuse.jpg


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16.4 Ports & Connectors:

Ports and connectors let the userconnect external devices like printers, keyboards, monitors or scanners

and let them interface with the PC (Personal Computer). The physical interfaces for the ports and con-

nectors are located on the outside of CPU cabinet but they are directly or indirectly (using a connector

card) connected to the motherboard. There are various types of ports or connectors, each providing dif-

ferent data transfer speeds to connect various external peripherals.

Parallel ports: Parallel ports are used to connect external input/output devices like scanners or print-

ers. Parallel ports facilitate theparallel transmission of data, usually one byte (8 bits) at a time. Paral-

lel ports use 25 pin RS- 232C.

Com/Serial ports: They are used for connecting communication devices like modems or other serial

devices like mouse, Keyboard. There are two varieties of Com ports the 9-pin ports and 25-pin ports.

Serial Ports facilitate the serial transmission of data, i.e. one bit at a time.

IDE drive connector: IDE devices like CD-ROM drivesor hard disk drives are connected to the

motherboard through the IDE connector.

http://en.wikipedia.org/wiki/File:RS-232.jpeghttp://en.wikipedia.org/wiki/File:Serial_port.jpghttp://en.wikipedia.org/wiki/File:Parallel_computer_printer_port.jpg


25/44


Floppy drive connector: The floppy drive connectors are used for connecting thefloppy drive to the

motherboard, to facilitate data exchange. Now a days floppy drives are hardly used by any personal

computers.

USB Port or connectors: USB stands forUniversal Serial Bus. This is latest and most popular port

technology. These ports provide the user with higher data transfer speeds for different USB devices

like keyboards, mouse, scanners or digital cameras.

PS/2 Connectors: PS/2 stands for Personal System/2. PS/2 connectors are used to connect PS/2 based

input devices likePS/2 keyboards or mouse.

Monitor Ports: The monitor port is used to connect monitor with the system. These are called as VGA

(Video graphic Array) connector

Power Connectors: These are used to connect the power chord from external power supply source,

from which the internal power supply connectors get the power to the mother board and other devices.

http://en.wikipedia.org/wiki/File:IEC60320_C13.jpghttp://en.wikipedia.org/wiki/File:IEC60320_C14.jpghttp://en.wikipedia.org/wiki/File:VGA_Stecker.jpghttp://en.wikipedia.org/wiki/File:VGA_port.jpghttp://en.wikipedia.org/wiki/File:Ps-2-ports.jpghttp://en.wikipedia.org/wiki/File:USB_TypeA_Plug.JPGhttp://en.wikipedia.org/wiki/File:USB_Connector.jpg


26/44


In addition to the common components that are found on the motherboard, newer motherboards also

come with integrated graphics accelerator cards or sound cards-there is no need to install a separate card

to get the work done.

View of Ports & Connectors

1.6.5 The Bus:

The maze of circuits etched on the motherboard forms the bus of the PC. A bus acts as the systems ex-

pressway -it transmits data between the various components on the motherboard.

Theoretically, a bus is a collection of wires through which data is transmitted between the various

components of a PC. A bus connects the various components of the PC with the CPU and the main

memory (RAM) logically, a bus consists of two parts, an address bus and a data bus.

The Data Bus: The Data Bus is an electrical path that connects the CPU, memory, and the other hard-ware devices on the motherboard. Actually, the bus is a group of parallel wires. Each wire can transfer

one bit at a time, an 8-bit bus can move eight bits at a time, which is a full byte. A 16-bit ISA (Industry

standard Architecture) bus can transfer two bytes, later 32-bit MCA (Micro channel Architecture) and 32

bit EISA (Extended Industry standard Architecture) bus was introduced these can transfer 4 bytes at a

time, present days 64 bits bus called as PCI (Peripheral component Interconnect) Bus is used.

PC buses are designed to match the capabilities of the devices attached to them. When CPUs could send

and receive only one byte of data at a time, there was no point in connecting them to a bus that could

move more data. As microprocessor technology improved, however, chips were built that could sendand receive more data at once, and improved bus designs created wider paths through which the data

could flow.

The Address Bus: The second bus that is found in every microcomputer is the address bus. The address

bus is a set of wires similar to the data bus that connects the CPU and RAM and carries the memory ad-

dresses.

The computer power is not only known for its speed, but also for its storage capacity. Computer memory

holding capacity is determined based on the size of Address bus. More width of an address bus more it

has the memory capacity.

Over the year the size of the address bus has been increased to 32 bits from 20 bits, a 32 bit address bus

system can address 4 GB of memory capacity.



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CA-IPCC-Information TechnologyControl bus :( or command bus) transports orders and synchronize signals coming from the control unit

and traveling to all other hardware components. It is a bidirectional bus, as it also transmits response sig-

nals from the hardware. A control bus is a computer bus, used by CPUs for communicating with other

devices within the computer.

It is used to transmit a variety of individual signals (read, write, interrupt, acknowledge, and so forth)

necessary to control and coordinate the operations of the computer. The individual signals transmittedover the control bus and their functions are covered in the appropriate functional area description.

1.7 Storage Devices

The CPU requires the basic instructions needed to operate the computer, but it does not have the capabil-

ity to store programs (Instructions) or large sets of data permanently. Just like human brain which stores

all the data, computer needs blocks of space where it can store the instructions that help in processing

arithmetical and logical operations. This area is called memory or storage.

1.7.1 Types of Storage Devices:

Various forms of storage devices are invented each with an individual purpose shown above

1. Primary Storage: Primary storage is either connected directly or a part of the CPU, this must be

present for CPU to function properly. As shown in the figure the primary storage consists below parts:



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CA-IPCC-Information TechnologyProcess Registers are internal memories of CPU. These are the fastest memories than all forms of com-

puter storage. Registers holds the information that the Arithmetic and Logic units need to carry out the

current instruction.

Main Memory Contains the programs that are currently being run and the data on which the programs

are executed. The ALU can very quickly transfer information between the process register and the loca-tion in main memory known as memory addresses. In present computer the RAM (Random Access

Memory) is used as main memory which is directly connected to CPU via Address bus and Data

bus.

Main Memory

Cache Memory is a special type of internal memory used by CPU for improving the performance and

output. This memory is used to hold those data and instructions which are frequently used by CPU. This

memory is used in limited capacity than RAM.

2. Secondary, tertiary and offline storage: These storage devices are used for Mass storage of data.

These storages are also known as permanent storage devices, where as primary storage is used to hold

the data temporarily till the processing completed.

Secondary storage requires the computer to use its input/output channels to access the information and

used for long-term storage of persistent information. Hard disks are the most popular secondary storagedevices. Time taken to access the data from Hard disks are much less than the time taken to access data

from Magnetic tapes, rotating devices like CD or DVDs.

Tertiary storage is removable storage devices like CDs and DVDs but the process of removing and

inserting the devices is carried out by Robotic arms automatically as per the operating systems instruc-

tions. These types of storages are not seen in the personal computers.

Offline storage is a system where the storage medium can be easily removed and inserted manually.

Offline storage can be used for data transfer, Back up or Archival purpose. In modern computers the off-

line storages are CDs DVDs and Flash Memory (Pen Drives, Memory cards etc.) In past the offline

storages are Magnetic tapes.

Robotic storage is a new type of storage method used for backups, and for high capacity archives in

imaging, medical, and video industries. Robotic-access storage devices may have a number of slots,

each holding individual media, and usually one or more picking robots that traverse the slots and load

media to built-in drives. The arrangement of the slots and picking devices affects performance.

3. Network Storage: A network storage system helps organize and save critical information created on

a computer in an efficient and accessible manner. The most basic form of network storage is saving a

computer's content to a disk or CD-ROM and storing it somewhere safe.



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CA-IPCC-Information TechnologyNetwork storage allows to centralize the information management in an organisation, and to reduce du-

plication of information. Network storage includes:

Direct Attached Storage (DAS) refers to a network storage system on which data is saved to the serv-

er computer's internal hard drive. The network workstations access the server to connect to the stor-

age.These files are saved directly onto the computer's disk space and can be readily pulled up at any time.

This is the most commonly used means of network storage.

The disadvantages of DAS include its inability to share data or unused resources with other servers.

Network Attached Storage (NAS) is a type of network storage system that saves data onto another

computer system attached to a group of computers through a network, or onto a special server at-

tached to the network.

A NAS device is typically a stand-alone, high performance, single purpose system or component.

It serves specific storage needs with its own operating system and integrated hardware and software.

NAS devices are well suited to serve heterogeneous networks.

The advantages of NAS over other methods of storage are performance and connectivity.

Storage Area Network (SAN) is an architecture to attach remote computer data storage devicesto

servers so the devices appear as locally attached to the operating system.

A SAN typically has its own networkof storage devices that are generally not accessible through the

regular network by regular devices.

SAN reduces data traffic and improves data access by using Fiber connections.

1.7.2 Characteristics of Storage: The different storages like primary, secondary, tertiary and offlinehave the below characteristics:

1. Volatility of information

Volatile memory requires the constant power supply to maintain the information; these are used as

mainly for primary storage. Once power is off the information stored in these will be erased automatical-

ly e.g. RAM.

Non-Volatile memory will retain the information that is stored even if power supply is off. It is suitable

for long term and permanent storages. Therefore these are used for Secondary, Tertiary and offline stor-ages. E.g. Hard disk, DVDs Pen drives.

Dynamic memory is volatile memory which also requires that stored information is

Periodically refreshed, or read and rewritten without modifications.

2. Ability to access non-contiguous information

Random Access means any location in storage can be accessed at any moment in the same amount of

time. This provides fast access to the data stored.

Sequential Access means accessing a piece of information sequentially i.e. one by one from the position

of last accessed information.



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3. Ability to change or delete information

Read/Write storage or Mutable storage allows information to be over written, modify, delete or re-

trieve the required information at any time, e.g. Hard Disk. Modern computers use these storages as Sec-

ondary Storage.

Read only storage retains information stored at the time of manufacture and Write Once Memory

(WROM) allows to write information only once at any point of time e.g. CD.

These are called Immutable Storage, mainly used for Tertiary storage and Offline back up storage. The

information stored in these cannot be changed.

Slow Write, fast read storage is read/write storage which allows information to overwritten multiple

times, but with the write operation being much slower than the read operation, e.g. Re-writeable

CD/DVD

4. Addressability of information

Location Address Storage: In this each individual character of information is given separate address

e.g. RAM

File Address Storage: In this information is divided into files and file is provided an address which is a

human readable. The underlying device still uses location address system but operating system will pro-

vide the file abstraction to make the operation more understandable

Content Address Storage: These are also implemented with the use of some software to address a par-ticular content or field like you look in your mobile for Dialed numbers, Missed calls, Received calls

etc.

5. Capacity and Performance

Storage capacity is the total size of the information that a storage device or medium can hold. It is mea-

sured as Megabytes (MB) or Gigabytes (GB).

Storage Density defines the compactness of stored information. It is measured as megabytes per square

inch or gigabytes per square inch.

Latency is the time taken to access the information from the storage device as we know Hard disk takes

less time to access the information than the Floppy. It is measured in millisecond, microsecond or

nanosecond etc.

Throughput is the rate at which the information can be read from or written to storage devices. It is

measured in the MB/sec GB/sec.

1.7.3 Primary Storage

Following are various types of system memories in the computer system. These are also known as on

board Memories i.e. memories on some circuit board.



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1. Semiconductor Memory: Semiconductor memories are in the form of thin chip known as Integrated

Circuit (IC). These memories are made with semiconductor material known as Silicon. There are vari-

ous technologies of semi-conductor memories, faster and more expensive bipolar semiconductors are

often used in Arithmetic Logic Units and high speed buffer storage sections of the CPU, while slowerand less expensive metal-oxide semi-conductors (MOS) are used in primary memory.

1) These memories are made with a semiconductor material known as silicon in the form of IC (chip).

2) These silicon chips consists of large no of transistors (Storage cells) that can hold the large capacity

of data

3) These memories are very fast in operation (no moving or mechanical part is used, as in Floppy or

Hard disk) and consume low power.

The ICs can be scaled according to the capacity of the chip used in storing the data in computer system:

SSI (small-scale integration): Up to 100 electronic components per chip.

MSI (medium-scale integration): From 100 to 3,000 electronic components per chip.


Primary Storage

Semiconductor

Memory

RAM ROM Bubble

Memory

Flash

Memory

Video

RAM

Dynamic

RAM

Static

RAM

PROM EPROM EEPROM


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CA-IPCC-Information Technology LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip.

VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip.

ULSI (ultra large-scale integration): More than 1 million electronic components per chip.

2. RAM (Random Access Memory):

1) The RAM is high speed semi-conductor memory, it is synonym with computer main memory i.e. all

the computers main memories or primary memories are known as RAM.

2) RAM is that memory in computer, that holds the instructions and data which are currently under ex-

ecution.

3) RAM is a volatile memory; the information in RAM will be lost once the power is switch off.

4) Data in the RAM can be accessed or insert directly, hence this memory is called as Random Access

Memory.

RAM can be of two types Static RAM and Dynamic RAM, discussed below:

The Static RAM retains the stored data as long as the power remains on, whereas with dynamic RAM,

the stored information disappears after a few milliseconds have elapsed, even when power is on.

The data must, therefore be repeatedly refreshed before it disappears. The power consumption of a dy-

namic RAM is less than that of a static RAM.

The computer does the refreshing process itself, taking time out from other chores every few millisec-

onds. It will read all the RAM memory positions while they are still readable and put appropriate new

charge on each capacitor. Some dynamic RAM memory circuits include built-in refresh circuits to re-

lieve the computer.

Presently used is DDR SDRAM (Double Data RateSynchronous DRAM) used for RAM chips and

SRAM are used forhigh speed but less storage capacity cache memory units.

Other Types of SRAM Asynchronous SRAM; Synchronous SRAM; Pipeline Burst SRAM.

3. ROM (Read Only Memory):

Another type of computer memory is the Read Only Memory it is used for the Micro programs. The

name implies that the data stored in this can only be read and cannot be altered by any regular programs.



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CA-IPCC-Information TechnologyThe information is stored permanently at the time of manufacture. These are used for storing permanent

instructions which computer may be executing frequently. One set of instruction found in ROM is

ROM- BIOS which stands for Read Only Memory Basic Input Output Services.

Types of ROM,

PROM: Programmable Read Only Memory is a non-volatile memory which allows the user to programthe chip with a PROM write. The chip can be programmed once, thereafter, it cannot be altered.

EPROM: EPROM stands for Erasable Programmable Read Only Memory. EPROM chips can be elec-

trically programmed. Unlike ROM and PROM chips, EPROM chips can be erased and reprogrammed.

Erasure is performed by exposing the chip to Ultra-violet light.

EEPROM: Electrically Erasable Programmable Read Only Memory is EPROM. However, the data can

be erased by applying electrical charges.

Rom is mainly used for storing system software and set of start up instructions for computer and some

micro program to control the computer hardware and these start up instructions and micro program are

known as BIOS.

4. Bubble Memory: This Bubble memory is composed of small magnetic domains (bubbles) formed on

a thin single-crystal film of synthetic garnet. These bubbles which are actually magnetically charged

cylinders which are thousandth of centimeter in size, can be moved across the garnet film by electric

charges. The presence or absence of a bubble can be used to indicate whether a bit is on or off. The

bubble memory is non volatile i.e. data will reside even power is turned off. Therefore, this memory can

be used for auxiliary storage. Since it is small, lightweight, and does not use very much power, bubblememory is finding a great deal of use as an auxiliary storage in portable computers.

5. Flash memory: Flash memory chips are one of the latest storage devices. These chips, a form of stat-

ic RAM (SRAM) chips, store data much like those used in the computers primary storage. However,

the data stays recorded even when the power is turned off flash memory is non-volatile. Since flash

memory devices have no moving parts, and are therefore very fast, they may eventually replace slower,

mechanical hard disk drives.

Flash memory is small in size portable memory, can easily carry in pocket, these are being used as auxil-

iary memory in small size PDA (Personal Digital Assistant), Palm Top computer and Digital Camera

etc.



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CA-IPCC-Information Technology6. Video RAM: This is a memory used for quality graphic display. It is normally part of AGP (Acceler-

ated Graphic Processor Card) and help in accelerating the display of graphics, special effects on the

screen. It does this by using two .ports,. one connected to the CPU and the other to the screen. Data

flows in one port and out the other very smoothly.

1.8 Secondary Storage:

Mainly there are two types of memory in computers. One is known as Primary memory and other is sec-

ondary memory or auxiliary storage. Primary storage is built into the CPU whereas secondary storage or

auxiliary storage is usually housed in a separate unit or units. Primary storage is very fast-its contents

can be accessed in millionth or billionths of a second. But primary storage has a limited capacity and

cannot store data permanently. In order to overcome these problems of primary memory computers al-

ways has a secondary memory to store data permanently. Secondary storage has an almost infinite ca-

pacity measured in millions and billions of bytes.

Primarily there are two types of auxiliary storage although there are Magneto Optical and semiconduc-

tor memories also which are used as auxiliary storage devices.

1.8.1 Floppy Diskettes:

In the early 1970.s IBM introduced a new medium for storing data. This medium consisted of a circular

piece of thin plastic material, approximately eight inches in diameter that was coated with an oxide ma-

terial. The circular piece of plastic, called a disk, is enclosed in a square protective jacket with a cut out

(Read/Write Slot) so that the magnetic surface is exposed for data storage and retrieval.

Diskettes are available in a number of different sizes. The original diskette was of the size of 8 inches.

During the 1980, most PCs used 5.25-inch diskettes. Today, the 3.5- inch diskette has largely replacedits 5.25-inch cousin. The size refers to the diameter of the disk, not to the capacity. As mentioned above

surface of diskette are coated with millions of small iron particles (Oxides) to store the data. Each of

these particle acts as a magnet. When read/write head of floppy drive passes over these magnets it gener-

ates magnetic field in these magnet to store data.

5.25 Floppy 3.5 Floppy



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Floppy Drive

Floppy diskette when inserted in the floppy drive will start doing the circular motion. Normal rotational

speed of floppy is 300 rotations per minute. Read/Write head of drive can do the linear movement only.

1.8.1.1 How Data is stored or organized on Floppy Disk:

When the new diskettes (or a new hard drive) are purchased, the disks inside are nothing more than sim-

ple, coated disks encased in plastic. Before the computer can use them to store data, they must be mag-

netically mapped so that the computer can go directly to a specific point on the diskette without search-

ing through data.

The process of mapping a diskette is called formatting orinitializing. Today, many diskettes come pre-

formatted for either PCs or Macs. The first thing a disk drive does when formatting a disk is to create aset of magnetic concentric circles called tracks.

Tracks & Sectors



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Magnetic material of disk which stores data is divided into concentric circles known as tracks. The

Tracks are further divided into sectors. Each sector has unique number on the disk, which help computer

to access or store data on floppy disk. Sectors are used ultimately to store or refer data on diskette. Now

a days 3.5 inch floppy is double sided (means both the sides can store the data), with 80 tracks per side

and 18 sectors per track with 512 bytes or 0.5 KB on every sector.

The Storage capacity of the diskette is dependent on the following three factors.

1. The number of sides on the diskette i.e. single sided or double sided now a days only double sided

diskette (which can store the data on both sides of diskette) are available in market

2. Recording density: Recording density refer to number of bits that can be stored on one inch of inner

most tracks known as bpi (bits per inch). Diskette can be single density (2768 bits per inch), double

density (5876 bits per inch) or high density (excess of 10000 bits per inch) now a day only high density

floppy diskettes are available in the market.

3. Number of Tracks: Number of tracks depends on the drive but now a days only 80 tack per side is

available in the market.

1.8.2 Magnetic Disk (Hard Disk):

Magnetic disks are higher version of Floppy. In place of using one plastic film of double sided as in

floppy, magnetic disc uses so many surfaces of metal plates which are more rigid than the plastic film in

floppy which will increase the storage capacity. Magnetic disk surface is also divided into tracks and

further divided into sectors. These so many surfaces together are attached on one simple like a stack of

disk. The same track no. of every surface is aligned and makes a structure known as cylinder.



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CA-IPCC-Information TechnologyUnlike floppy diskettes, where the disk and drive are separate, the hard disk and drive is a single unit. It

includes the hard disk, the motor that spins the platters, and a set of read/write heads. The terms hard

disk and hard drive are used interchangeably as the drive and disk cannot be separated.

These Stack of surfaces keeps the read and write head (each surface has on read/write head) to read and

write data from and to surface. In there are pack of 5 discs with two surfaces each side then there will be10 surfaces to store data. The number of read/write head will be equal to number of surfaces used for

storage purpose.

Magnetic discs are the most popular direct access medium. The capacity of the magnetic disk is much

larger than the floppy disk. Normal capacity of the floppy disk is 1.44 MB whereas in present days the

magnetic disk which is popularly called as hard disk is of 200 GB to 500 GB, 1 Terra byte or more. Per-

formance wise also the magnetic disk will access the data at much higher speed than the floppy because

of its hard metal surfaces the rotational speed of magnetic disk is much higher than floppy disk. The

hard disk spins 3600 rpm and 7200 rpm instead of floppy diskettes 300 rpm.

Magnetic disks are packed in the air tight vacuum chamber to make it more reliable and less prone to

damage because of its non exposure to dust, air, moisture etc,.

1.8.2.1 Data Storage

Not only do hard disks pack data more closely together, they also hold more data, because they often in-clude several platters, stacked one on top of another. To the computer system, this configuration just

means that the disk has more than two sides; in addition to a side 0 and side1, there are sides 2, 3, 4 and

so on. Some hard disk drives hold as many as 12 sides, but both sides of the disks are not always used.

With hard disks, the number of read/write heads specifies the number of sides that the disk uses.

Hard Disk



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CA-IPCC-Information TechnologyFor example, a particular hard disk drive might have six disk platters (that is, 12 sides), but only eleven

heads, indicating that one side is not used to store data. Often, this is the bottom side of the bottom disk

The computation of a hard disks capacity is identical to that for floppy diskettes-but the numbers are

larger. The breakdown of the storage capacity for a disk is given below:

Storage Capacity = No. of recording platters x No. of tracks per platter x No. of sectors per track x No.

of bytes per sector.

For Example, a disk has 12 plates each having 3000 tracks. Each track is having 200 sectors per track,

and each sector can store 512 bytes. The total recording surface would be 11 (total 22 recording sur-

faces, 11 x 2) since upper and lower disk surface does not have recording (r/w) heads.Total storage capacity = 22 x 3000 x 200 x 512 i.e.675,840,0000 bytes which is equivalent to approxi-

mately 6 GB of data.



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CA-IPCC-Information TechnologyThe time required to access any data from disk is known as access time. This time is made with three

components.

1. Seek Time: Time taken by read/Write head to move itself from its present position (track) to position

from which data is to be accessed.

Read/Write head moving from one track to another

2. Rotational Time: Time taken by disk to move itself rotationally and position the start point of data

under the head. AverageRotational time or Latency time is equal to the time taken in half of disk rota-

tion.

3. Data Transfer Time: Time taken to transfer the read data from secondary storage to primary memo-

ry.

The total of these three components is known as the access time and typically ranges from, 8 to 12

milliseconds.

1.8.2.2 Advantages and disadvantages of magnetic diskThe hard disk is most popular auxiliary storage which is used in almost all the micro and personal com-

puters, notepads, laptops etc,. Inspite of its popularity and advantages it has its own disadvantages. Be-

low are the advantages and disadvantages of the Magnetic disk.

The advantages of magnetic disk include:

1. Magnetic rigid disk is direct access storage medium; therefore, individual records can be retrieved

without searching through the entire file.

2. The costs of disks are steadily declining.

3. For real-time systems where direct access is required, disks are currently the only practical means of

file storage. Other new types of storage, such as bubble storage, are not widely used yet.

4. Records can be readily updated by writing the new information over the area where the old informa-

tion was stored (Overwriting of the old data).

5. Interrelated files stored on magnetic disk can allow a single transaction to be processed against all of

these files simultaneously, without reentry and reprocessing of instructions.

The Disadvantages of magnetic disk include:

1. Security of information stored on magnetic disks which are used as shared, is major concern.



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2. Regular 'head' crashes can damage the surface of the disk, leading to loss of data in that sector.

3. When new data is stored in magnetic disk, it is stored with a technique known as overlaying in which

new data is stored on old data as a new layer; this will erase the old data. With this type of storage we

lack in Audit Trail of previous stored data.

4. Magnetic disk is generally fixed into cabinet and connected to the mother board through cables, so it

cannot be moved so easily from one place to another.

1.8.3 Optical Laser Disks

These are capable of storing vast amount of data, these uses the laser beams instead of read/write head.

One laser beam writes the data on to the recording surface and another laser beam is used to read the

data.

These are highly reliable, compact in size and inexpensive. These disks are circular in shape and divided

into tracks, normally contain large no. of tracks.

These are sequential storage and direct access medium that is one can access any of the tracks on the

disk directly.

The below are the categories of Optical laser disks, CD ROM disks; WORM disks, DVD, and Blu-Ray

1. CD ROM:

This one is the most popular type of optical disk in the market. First of all invented by Phillips Compa-

ny, initially these memories were used for audio data for recording and distribution music. But very soon

CDs become very popular medium to store and retrieve computer data because of its high capacity, high

reliability and low cost. Most of the compact disks in the market are read only disks. That is once data iswritten on these disk cannot be altered.

CDs are very inexpensive medium to store large amount of data, a CD cost 10/- can store data of 650

MB. CDs have become universal memories for distributing software. CDs are used for storing all types

of data like audio, video, text or any other type of commercial data.

Because of its low cost and high reliability it is used as universal portable type of memory for transfer-

ring software and data from one place to another. Now a days CD manufacturer has also introduced the

CD-RW that is compact disk Rewritable which allow a CD to be written again and again just like flop-py. CD RW are similar to floppy features but has additional high storage capacity and more reliability

and retaining capability of data.

Internet becoming more and more usable medium for sharing information and information containing lot

of graphics which require high memory capacity. In order to save these high memory data for longer du-

ration of time the CD-RW would become a necessity and would replace the use of floppy disk.

Finally, we can say CD has gone following technological changes

CD-ROM (Compact disk Read Only Memory) known as Pre-recorded CD

CD-R (Compact disk Recordable) known as once recordable CD

CD-RW (Compact disk Rewritable) known as Rewritable CD



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CA-IPCC-Information TechnologyCompanies like Samsung, LG, manufacture the CD-ROM drive and CD Writer.

2. WORM Disks: These are optical memories known as Write once Read Many Times Disks. These

memories are like CD-R and used for storage of historical data permanently. These disks used to have

approx 200 MB capacity for storage of text and image data.

Access times for CD-ROM and WORM drives tend to be quite slow by hard disk drive standards, rang-

ing from 100 to 300 milliseconds.Another popular application of WORM disks is in information systems that require the merging of text

and images that do not change for a period of time. A good example is an electronic catalogue

3. Magneto-Optical Disks and Drives: This Disk integrates the technology of both optical and mag-

netic disks. The disk has the advantage of optical disk of large capacity and re-writable advantage of

magnetic disk. Magneto-optical disk can store approx 1000 MB of data. The drive required for this disk

reading and writing is magneto optical drive.

This disk is not a popular storage medium and not much in use due to its high cost.

For rewriting the data on magneto optical disk the data can be erased first and write new data or as in

hard drive new data can be written by overwriting the old data which provides a fast data storage.

4. DVD (Digital Versatile Disks or Digital Video Disk): This one is most popular invention in the

family of optical disk. These memories absolutely resemble like CD but can store much large amount of

data than CD. These memories can store and reproduce the data particularly graphics and video data

with a very high quality in comparison to CD. DVD surfaces are divided into Tracks and one can access

any of these tracks in no time that is access rate of DVD is much higher than the floppy.

Unlike CD, DVD can store the data on both sides and can have two layer on each side to give larger ca-

pacity. One DVD can store upto 17 GB capacity. There are predictions that DVD would replace hard

disk as storage media because of its high capacity, reliability and quality. Right now most of the use of

DVD is in storing audio and video data for various applications, like in entertainment industry and vari-

ous industrial training applications.



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Similar to CD evolutions, DVD has also undergone technological improvements from DVD (Read only)

to DVD RW.

DVD (Digital Video Disk) this is Read only storage medium

DVD-R (Digital Video Disk Recordable) this can be recorded only one time.DVD-RW (Digital Video Disk Rewritable) known as rewritable DVD.

Various types of DVDs can be used for storing images, text, movies, high resolution graphics etc.

1. DVD-5 holds 4.7 GB data and is supported by the DVD+R/RW and DVD-R/RW formats. It

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Info Tech - Chapter 1