Fundamentals of Cs[1]

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Unit I Introduction to Computers Page 1 of 70

Nizam College, B.Com (eCom) I year I Semester Sarah M.

B.COM I YEAR (E-Com)SEMESTER-I

FUNDAMENTALS OF INFORMATION TECHNOLOGYPaper Code No: 104 COME Max. Marks: 50

PPW: 4 (30 Theory + 20 Practical)

UNIT I: INTRODUCTION TO COMPUTERS

Brief History of ComputersGenerations of computersElements/Components of Computer

Central Processing UnitMain Memory UnitArithmetic and Logic unitControl Unit

Random Access Memory (RAM)Read Only Memory (ROM)Programmable Read Only Memory (PROM)Erasable Programmable Read Only Memory (EPROM)

Input / Output Devices

Magnetic TapeMagnetic DiskFloppy Disk, etc

MonitorTerminals

PrinterPlotterCD ROM

Impact of computers on Business and SocietyFlow charting concepts


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Introduction to Information Technology

Information technology (IT) may be defined as the technology which is used to acquire, store, organize, and processdata to a form which is usable in specified applications, and disseminate the processed data. Information isprocessed data based on which decisions can be taken and appropriate actions initiated. Information is alsoprocessed data which improves out knowledge enabling us to do out work better.

Information Technology

Definition: the study, design, development, implementation, support or management of computer-based informationsystems, particularly software applications and computer hardware

It refers to anything related to computing technology, such as networking, hardware, software, the internet or thepeople that work with these technologies.

Components of Information Technology

Use and implementation of IT involves various components: hardware, software, data, users, storage andcommunication:

(a) Hardware Hardware are those tangible components, of a computer which one can see and feel. E.g. inputdevices, output devices, CPU etc.

(b) Software software are set of instructions or programs which are given to computers so that it works anddoes the task.These are those intangible components of computer that makes the tangible components work.

(c) Data It is the collection of facts and figures which has to be worked on by the computer.(d) Users these are those people who directly or indirectly are benefited by the use of computers. They are

users of final output as well as the providers of input.(e) Storage this component is the one which enables the data and software components to make its space in

the computer system by residing in various types of storage devices. These data storage components helpthe raw as well as processed data (information) to be stored for further usage.This component is also known as memory.

(f) Communications this is that component which enables a user to communicate with the computer as welas the computer to communicate with the other computer to get various tasks done.

Introduction to Computers

Definition: a computer is an electronic device that processes given data to derive the required and usefuinformation.

A computer is an electronic machine that accepts information, stores it until the information is needed, processesthe information according to the instructions provided by the user, and finally returns the results to the user. Thecomputer can store and manipulate large quantities of data at very high speed, but a computer cannot think. Acomputer makes decisions based on simple comparisons such as one number being larger than another. Althoughthe computer can help solve a tremendous variety of problems, it is simply a machine. It cannot solve problems on

its own.

Data, Information and Knowledge

Data Data items refer to an elementary description of things, events, activities, and transactions that are recordedclassified, and stored, but not organized to convey any specific meeting. Data items can be numeric, alphanumeric,figures, sounds, or images. A student grade in a class is a data item, and so is the number of hours an employeeworked in a certain week. A database consists of stored data items organized for retrieval.


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The word data refers to raw facts that have been collected from various sources but not organized. Suchdata cannot be used to make useful decision but when arranged it may provide meaningful information.

Information Information is data that have been organized so that they have meaning and value to the recipient.For example, a students grade point average is information. The recipient interprets the meaning and drawsconclusions and implications from the data. Data items typically are processed into information by means of anapplication. Such processing represents a more specific use and a higher value-added than simple retrieval and

summarization from a database.

Information may be considered as data that has been organized and processed. Information increasedunderstanding and helps people in making intelligent decisions.

The application might be a Web-based inventory management system, a university online registration system, or anInternet-based buying and selling system.

Knowledge Finally, knowledge consists of data and/or information that have been organized and processed toconvey understanding, experience, accumulated learning, and expertise as they apply to a current problem oractivity. Data that are processed to extract critical implications and to reflect past experiences and expertise providethe recipient with organizational knowledge, which has a very high potential value.

Data versus Information

Data Information

raw facts no context just numbers and text

data with context processed data value-added to data

summarized organized analyzed

Example 51007

Example 5/10/07 The date of your final exam.

$51,007 The average starting salary of an accounting major. 51007 Zip code of Bronson Iowa

Example

6.34 6.45 6.39 6.62 6.57 6.64 6.71 6.82

7.12 7.06

ExampleSIRIUS SATELLITE RADIO INC.

$5.80

$6.00

$6.20

$6.40

$6.60

$6.80

$7.00

$7.20

1 2 3 4 5 6 7 8 9 10

Last 10 Days

Stock

Price


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Data Processing

In past, manual techniques of collecting, manipulating and distributing data to achieve certain objectives wereknown as data processing.

When electro-mechanical devices were introduced to perform some of these functions, it was called asautomatic data processing (ADP)

These days, electronic computers are used to perform the same functions and hence this process is calledelectronic data processing (EDP)

To derive useful information from data, any method of data processing should consist of the following steps: Input,Processing and Output

Input is the process of capturing data and getting it into a form understandable to the computer Processing involves the various steps taken by the computer to manipulate the data in order to get useful

information Output is the step where the result obtained by the computer are made available to the user in human-readable

form

What is a computer?

We can define computer as "a device that processes given data to derive the required and useful information"During the processing the computer has to perform various functions like

(a) Accepting instructions from the user.(b) Accepting data from the user.(c) Performing various arithmetic and logical operations as per instructions given.(d) Presenting the information or output to the user.

Characteristics of a Computer

Computers are becoming popular day to day because of their characteristics which make them the most popularThe characteristics, which make the computer indispensable, are:

Fastness Computer is able to process the data and give the output in fractions of seconds such that requiredinformation is given to the user on time enabling the user to take right decisions on right time. A powerful computeris capable of executing about 3 million calculations per second.

Accuracy Inspite of its high speed of processing, errors seldom occur, as computers accuracy is consistently highenough which avoids any errors. If at all there are errors, they are due to errors in instructions given by theprogrammer, inaccurate and inconsistent data or defective programs as well defective system designs.

Output

Data InformationProcessing by Computer

Collection, Checking andPreparation (Sorting of Data for Further Use)

Input

Example: Details of hours workedby employee

Example: Name of Employee,Basic Pay etc.

Example: Pay Slips


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Reliable The output generated by the computer is very reliable, but it is reliable only when the data, which ispassing as input to the computer and the program, which gives instructions are correct and reliable. Inconsistent,incorrect and unreliable programs and data make the computer erroneous and unreliable i.e. if you want thecomputer to be reliable the input should be reliable. The popular phrase "Garbage in-Garbage out" i.e. GIGOrepresents the reliability constraint of the computer.

Large storage capacity The basic problem of pre-computer era was the storage of voluminous data which

required large amount of paper and storage space, such that even the storage and retrieval of data becomes aHerculean task. The computer has solved this problem by giving a provision to store large volumes of data in smalstorage devices, which have capacity to store huge amounts of data and help the retrieval of data an easy task.

Versatile The computer performs three basic operations. At first instance, it is capable to access and accepinformation through various input-output devices from the user. Secondly, it performs basic arithmetic and logicaloperations on data as desired. Finally, it is capable to generate the desired output, in the desired form. We can saythat is it the programming technique, which makes the difference by reducing given problem into an interplaybetween the above operations. It can work upon numbers, graphics, audio, video etc. making it really versatile.

Works automatically Computer is a device, which is much more than a Calculator, which is capable to do variousarithmetic operations and need a human operator to press the necessary keys for any operation to be performed.Whereas computer is different in working, once the instructions in form of program are fed to the computer it worksautomatically without any human intervention until the completion of execution of program or until it meets logicalinstruction to terminate the job.

Diligent As computer is a machine, it does not feel tired and distracted. Its performance is consistent even to anextent of more than 10 million calculations; it does each and every calculation with same speed and accuracyHence, for a quality performance, the computer comes as a healthy help.

Intangible benefits Computers give many intangible benefits like flexibility, ability to accommodate changes andexpansion, competitive advantage, better services can be provided, people may be served in a jiffy without muchhassle etc.

Cost Reduction Inspite of the cost of computerization, which is being coming down drastically over years, the

benefits which computers give, override the costs, thereby making the cost incurred to be recovered within no time,in turn reducing the effective cost, thus one can have competitive edge over others. It also attracts more and morepeople to go for computerization to reduce other costs of data processing and retrieval, which they have beenincurring all the times.

No emotional, ego and psychological problems As computers are machines they do not come with anyemotional, ego and psychological problems, which are otherwise destructive in nature, we may not neglect this frontbecause above all, these are the things which are the major causes of problems arising in an environment.

Thus with above characteristics computers do have a strong point to enter every sphere of life, but as all have someor the other limitations, as nothing in this universe is perfect, computers do have some limitations, which still do noover shadow the advantages of computers.

Limitations of computer

1. Computer does not work on itself; it requires set of instructions to be provided for, else computer (hardwareis a waste.

2. Computers are not intelligent, they have to be instructed about each and every step which they have toperform i.e. each and every task to be performed by them should be given in detail.

3. Computers cannot take decisions on its own one has to program the computer to take an action if someconditions prevail.

4. Computers, unlike humans cannot learn by experience.


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History of Computers

Eversince the man thought of counting, he developed the concept of computations. His initial approach toaccounting and data computations and their recording was with help of sticks, pebbles or lines on walls of cavesThen he moved towards counting using ten fingers of his hands, which probably is the basis of present decimasystem.

We can classify the historical evolution if computers in three different ways:

1. Early calculating devices2. Mechanical calculating machines3. Early computers

The following table shows the evolution of computers from calculating devices to computers:

YEAR INVENTION INVENTOR DESCRIPTION

EARLY CALCULATING DEVICES

450 BC ABACUS EgyptiansA wooden frame with balls/beadsstrung on parallel wires. Abacus isa semi mechanical calculator.

1614(17th Century)

LogarithmsNapiers Bones

John NapierScottish Mathematician

Invented logarithms also derived aset of 11 rods having 4 faces whichwere carved from bones are oftencalled Napiers Bones

1620 Slide RuleWilliam OughtredEnglish Mathematician

Based on the principle oflogarithms, slide rules consists of 2graduated scales, 1 of which slipsupon the other. Suitable alignmentof one scale against other makes it

possible to calculate just byinspection.

MECHANICAL CALCULATING DEVICES

1642Mechanical CalculatingMachine

Blaise PascalFrench Mathematician

Numbers were entered in thismachine by dialing a series ofnumbered wheels and a series oftoothed wheels transferred themovements to a dial which showedthe result.

1671 Calculating MachineGottfried Von LeitonitzGerman Mathematician

Machine which was able to perform

multiplication and division based onthe same principle of toothedwheels but added a new feature aseries of slider forming a shiftmechanism.

1822 Difference EngineCharles BabbageProfessor of Mathematics(Cambridge University)

Built for a Royal Society; used toperform computations needed forsetting up trigonometric andlogarithmic tables.

1833 Analytical Engine Charles Babbage It had a punched card input, a


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Professor of Mathematics(Cambridge University)

memory unit/store, n arithmeticunit/nil and an automatic print out.

1847-54 Boolean AlgebraGeorge BooleEnglish Mathematician

An algebraic system also known asBoolean Algebra used forrepresenting and manipulatinglogical expressions.

1889 Census Machines Herman Hollerith

Cencus machine would handle 50-

80 punched cards per minute.It waschosen for tabulating the 1890census & resulted in quicktabulation.

1920 Digital Calculating MachineLeonardo TorresParis

Leonardo Torres demonstrated adigital calculating machine in parisin 1920.

1931 Z-1, Z-2, Z-3 & Z-4Konrad ZuseGerman Engineer

Zuse introduced a computerSystem which used binary numbersystems as well systems whichworked on programs where z-3used binary system & z-4 was

program controlled.

EARLY COMPUTERS

1944 Mark-I Howard H. Aiken

Machine that automaticallyperforms sequence of arithmeticoperations; contained 72 addingaccumulators and 60 sets ofswitches, buttons, wire plugboards & punched tape.

1946 ENIAC (Electronic NumericalIntegrator & Calculator)

John Mauchly &Presper Eckert

First electronic calculator; Nomoving parts except 1/0 occupies9*15 m room space; 18000 vacuum

tubes; 1500 relays weighted 30tons; performed 5000additions/sec; consumed 150kw ofpower & needed to be watercooled.

1947-50EDVACI (Electronic DiscreteVariable AutomaticComputer)

Moore School Personnel& Ballistics Research Labof US Army

Internal storage technology

1949EDSAC (Electronic DelayStorage AutomaticComputer)

University of Manchester(English)

Apart from having Internal storagetechnology, it was the firstcomputer to contain a changeableprogram of instructions within its

own memory.

1951UNIVAC-I (UNIVersalAutomatic Computer)

Remington RandCommercial version of storedprogram computer which was firstdigital computer.


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INPUTUNIT

INPUT OUTPUT

INFORMATION

MEMORYUNIT

CONTROLUNIT

ARITHMETICLOGIC UNIT

OUTPUTUNITDATA

C.P.U.

Parts of Computer System

Block Diagram of Computer

1. Input Unit

When using a computer the text of programs, commands to the computer and data for processing have to beentered. This requires the use of input units/devices.

An input device is a hardware mechanism that transforms information in the external world for consumption by acomputer. Typical examples of input devices include keyboard and mouse.

2. Central Processing Unit

Once the data is accepted it is fed into central processing unit before the output is generated as data has to beprocessed which is done by CPU. This unit is the brain of computer system, which does all the processing,calculation, problem solving. The CPU consists of the following three distinct units, namely:

Memory Unit This is the unit where the data and results are stored. The major function of this unit is toremember the instruction and data. The data stored can be accessed and used whenever required bythe CPU. It controls the flow of data to and from the main storage.

Control Unit This is that unit of CPU, which coordinates with all the activities of each and everyelement of computer. It decodes the instructions given by various users and its sends commands andsignals.

Arithmetic and Logic Unit This unit performs the arithmetic operation such as addition, subtractionmultiplication and division. It also does logical operations such as comparison of numbers etc.

3. Output Unit

Information has to be returned from the computer to the user after processing. This requires the use of outputunits/devices.


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Any device that presents output from the computer is called an output device. It is an electronic orelectromechanical equipment connected to a computer and used to transfer data out of the computer in the form otext, images, sounds or other media to a display screen (monitor), printer, loudspeaker or storage device.

Input and output devices together make up the hardware interface between a computer and the user or externaworld.

Storage or Memory

A computer can function with only processing, memory, input and output devices. The purpose of storage is to holddata permanently.

The memory of a computer can hold program instructions, data values, and the intermediate results of calculationsAll the information in memory is encoded in fixed size cells called bytes.

When referring to a computers memory, the numbers are often so large that it is helpful to use terms such askilobytes (KB), megabyte (MB), gigabyte (GB) and terabyte (TB).

Unit Equivalent

8 bits 1 byte1,024 bytes 1 KB

1,024 KB 1 MB

1,024 MB 1 GB

1,024 GB 1 TB

Personal Computers (PC) have 128 MB of RAM.

Types of Memory

There are two main categories of memory; characterized by the time it takes to access the information stored there,the number of bytes which are accessed by a single operation, and the total number of bytes which can be stored.

i) Main Memory or Primary Memory or Volatile Memory is the working memory of the CPU, with fast accessand limited numbers of bytes being transferred. The main memory of the computer is also known as RAMstanding for Random Access Memory. It is constructed from integrated circuits and needs to have electricapower in order to maintain its information.

When power is lost, the information is lost too! It can be directly accessed by the CPU. This is broadly comparable with the speed at which the CPU will need to access data. Main memory is expensive compared to external memory so it has limited capacity.

ii) Secondary Memory or External Memory is for the long term storage of information. Data from externa

memory will be transferred to the main memory before the CPU can operate on it. Access to the externalmemory is much slower, and usually involves groups of several hundred bytes.

External memory which is sometimes called backing store or secondary memory, allows the permanentstorage of large quantities of data.

It has an important property that the information stored is not lost when the computer is switched off. The most common form of external memory is a hard disc which is permanently installed in the computer

and will typically have a capacity of hundreds of megabytes.


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Classification of Computers

Computers can be classified based on the following:

Based on electronic technology

o First generation of computerso Second generation of computerso Third generation of computerso Fourth generation of computerso Fifth generation of computers

Based on working principles

o Analog computero Digital computero Hybrid computer

Based on purpose

o General-purpose computero Special-purpose computer

Based on functional capabilities (Speed, Size, Memory Capacity)

o Microcontrollerso Microcomputers

Personal computerso Desktop and Tower Unitso Laptop

Notebook Computer Sub-notebook Computer

o Pocket PCs Electronic organizers Palmtop computers Pen computers

o Personal Digital Assistant (PDAs)

Workstations

o Minicomputer/Mid-ranged computers

o Mainframeso Supercomputers

Based on number of users

o Single usero Multiuser


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BASED ON ELECTRONIC TECHNOLOGY

Generations of Computers

The development of computers has followed different steps in the technology used and these steps of technologicaldifferences are called as GENERATIONS in computer terminology. There are totally five generations of computerstill today:

First generation computers 1945-60Second generation computers 1961-65Third generation computers 1966-70Fourth generation computers 1971-89Fifth generation computers 1990-till

First Generation Computers (1945-60)

The first generation of computers was those computers, which used vacuum tubes (valves) technology. Almost althe early computers like ENIAC, EDVAC, EDSAC etc., were made a reality only by the invention of "Vacuum Tube"which is a fragile glass device that can control and amplify electronic signals. The machine language was the

language of these computers. The major advantage of the vacuum tube technology is that it made the advent ofelectronic digital computers. Vacuum tubes were only electronic devices available during those days which madecomputing possible.

Features of First Generation Computers

The general technical features of the computers belonging to this generation are:

1. The vacuum tubes were used in the circuits of these computers.2. The input and output operations were done using punched card technology.3. For external storage, magnetic tapes were used.4. The machine was capable to do one job at a time, therefore batch processing was adopted5. The operation like setting of switches has to be done by humans.

6. The language used by these computers was machine language and assembly language.

Example of Computers: UNIVAC-I, IBM 650 etc.

Limitations of First Generation Computers

1. Their operating speed was very slow and they had restricted computing capacity.2. They consumed high power and generated great amount of heat.3. They were bulky and required large space.4. They had a short span of life.5. The programming capabilities were limited.6. They were not very reliable.

7. Frequent breakdowns were common.8. They had small primitive memories and no auxiliary storage.

Later, these first generation computers were improved and they adopted a new technology for the main memorycalled magnetic core. UNIVAC and Leo are computers belonging to first generation of computers.

Second Generation Computers (1961-65)

With the development of transistors and their use in circuits, magnetic core for memory storage, the vacuum tubesof first generation are replaced by transistors to arrive at second generation of computers. The size of transistors is


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much smaller when compared to vacuum tubes; they consumed less power, generated less heat and are faster andreliable. The major advantage of use of transistors was that the size of computer has come down as well as thepower consumption. Even the cost of transistors is less in comparison with the cost of vacuum tubes, the cost ofcomputer reduced drastically, they were more reliable than first generation computers.

Features of Second Generation Computers

With invention of transistors by Bell Telephone Labs., the vacuum tubes of first generation were replaced bytransistors. The following were technical features of these computers of second generation:

1. Transistors were used in the circuits.2. The input operations were performed using punched cards and magnetic tapes and for output operations

punched cards and papers were used.3. For external storage magnetic tapes were used.4. The orientation was towards multiple users i.e. the machine was capable to process multiple tasks

concurrently.5. For punched card operations only, human intervention is required.6. High-level languages like FORTRAN, COBOL, BASIC etc. were used as the languages by the computer.

Example of Computers: IBM 1400 and 7000 series, General Electric 635 etc.

Third Generation Computers (1966-70)

With the development of silicon chips, the third generation of computers carne into existence. These computers usecompact integrated circuits (ICs) of silicon chips in place of transistors. Each of these integrated circuits consisted olarge number of chips in very small packages. With these ICs coming into picture the size of computers cost, heageneration and power consumption decreased to a great extent, speed and reliability increased as compared toprevious generations. These machines used ICs with large scale integration (LSI).

Features of Third Generation Computers

This generation of computers witnessed major advances and changes in hardware and software capacity. The

major technological features of computers of this generation are:

1. Integrated circuits replaced transistors. Inspite of their smaller size they were capable to perform better thantransistors.

2. For data input and output operations monitors and keyboards replaced the punched cards.3. For external storage magnetic disks were used.4. Sophisticated operating systems which were capable of handling several jobs concurrently were used.5. More advanced high level languages like PASCAL were used.

Example of computers: IBM System/360.

Fourth Generation Computers (1971-89)

The computers belonging to this generation used integrated circuits with very large scale integration (VLSI). Thesecomputers have high processing powers, low maintenance, high reliability, and very low power consumption. Thesecomputers have reduced the cost as well the size has come down drastically.

Features of Fourth Generation Computers

With the very large scale integration (VLSI) getting developed, microprocessors were created, which revolutionizedthe computer itself. The following are the technological features of the computers of this generation:


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1. The circuits used VLSI and microprocessors of virtually microscopic size, which led to drastic cut on the sizeof computer.

2. The input output devices were the same monitors, keyboard, printer etc. but with refinement.3. Microcomputers have evolved.4. Magnetic disks were the primary devices used for external storage.5. The use of special software for maintaining large data bases became popular.6. The application software for microcomputer essentially became popular in this generation.

Example of computers: IBM Systems/370, Burroughs B7700 etc.

Fifth Generation Computers (1990-till)

These computers use optic fiber technology to handle Artificial intelligence, Expert systems, Robotics etc. Thesecomputers have very high processing speeds and are more reliable.

Features of Fifth Generation Computers

The computers of this generation use optic fiber technology to handle Artificial Intelligence. These computers havecapacity to think and reason (intelligence being programmed) which can be used to solve problems where human

intelligence is required. Thus a fifth generation computer can handle various jobs with a great precision. ExpertSystems are examples of systems implementing Artificial Intelligence (AI).

BASED ON WORKING PRINCIPLES

A computer can be categorized as either analog or digital. Today, the word computer refers only to a digitacomputer and the functions, activities and organizations of computers explained are pertaining only to a digitacomputer. Based on working principles, a computer can be classified into the following types:

Analog computer Digital computer Hybrid computer

Analog Computers These are the computers, which operate on the principle of creating a physical analog ofmathematical problems. These computers continuously measure physical variables. These computers use signalsas input, which can come from devices like thermometers, speedometers, barometers etc. These signals arecontinuous flow of physical quantities, e.g. temperature, speed, pressure etc. which vary continuously. The resultgiven by these computers usually is not very precise, accurate and consistent. Because of the nature of operationtheir use is limited. Speedometer of a vehicle can be a good example of analog computers, where the speed variescontinuously.

Digital Computers These are the computers which accepts digits and alphabets as input, which are used forsolving, controlling any problem which can be expressed mathematically. These computers take data in form ofdiscrete signals representing ON [high] or OFF [low] voltage state of electricity. The data input can be representedas sets of O's and l's representing low and high respectively. These computers convert data into discrete formbefore operating on it. Digital watches can be a good example of digital computer, as the time, which is displayeddoes not vary continuously but changes from one discrete value to the other. The term "Computer" used in our day-to-day life is a reference to the digital computer only.

Hybrid Computer A computer that performs operations based on both analog and digital principles is called as ahybrid computer. In other words, a computer system that has capabilities, behaviors, functions and principles of bothanalog and digital computer is called a hybrid computer. E.g. ultrasonic digital scanner

The analog signals generated by the scanner (continuous voltage) are digitized (periodically measured andconverted to numbers) and supplied to a small digital computer.


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BASED ON PURPOSE

A computer system may be classified in the following manner on the basis of its purpose and its applications:

o General-purpose computero Special-purpose (dedicated) computer

General-purpose digital computers These are those computers which can theoretically' used for any type ofapplications. These computers can be used in solving a business problem as well mathematical equation with sameaccuracy and consistency. Most of the computers now are general-purpose digital computers. All the PCs, whichhave become almost every household affair, are all general-purpose digital computers.

Special purpose digital computers These are those digital computers, which are designed, made and used foany specific job. These are usually used for those purposes, which are critical and need great accuracy andresponse like satellite launching, weather forecasting, ignition instruments etc.

BASED ON FUNCTIONAL CAPABILITIES (SPEED, SIZE, MEMORY CAPACITY)

Computer systems based on functional capabilities such as architecture of the CPU, processing speed, capacity of

main memory and external storage devices, speed of output devices, number of users and cost, can be classified inthe following forms:

M I C R O C O N T R O L L E R S

M I C R O C O M P U T E R S

Microcomputers Personal Computers

Microcomputers are small computers that can fit on or beside a desk or are portable. Microcomputers arcconsidered to be of two types: personal computers and workstations.

Personal computers (PCs) are desktop, tower, or portable computers that canrun easy-to-use programs such as word processing or spreadsheets. PCs comein several sizes, as follows.

Desktop and Tower Units: Even though many personal computers today are portable, buyers of new PCsoften opt for nonportable systems, for reasons of price, power, or flexibility. For example, the television-tube-like (CRT, or cathode-ray tube) monitors that come with desktops have display screens that are easier toread than those of many portables. Moreover, you can stuff a desktop's roomy system cabinet with add-oncircuit boards and other extras, which is not possible with portables.

Microcontrollers, also called embedded computers, are t the tiny, specializedmicroprocessors installed in "smart" appliances and automobiles. Thesemicrocontrollers enable microwave ovens, for example, to store data about howlong to cook your potatoes and at what temperature.


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Tower PCs are those, in which the system cabinet sits as a "tower" onthe desk or on the floor next to the desk, giving you more usable deskspace.

Desktop PCs are those in which the system cabinet sits on a desk, withkeyboard in front and monitor often on top. A difficulty with thisarrangement is that the system cabinet's "footprint" can deprive you of afair amount of desk space.

Laptops: A laptop computer is a portable computer equipped with a flatdisplay screen and weighing about 2-11 pounds. The top of the computeropens up like a clamshell to reveal the screen. The two principal types oflaptop computers are notebooks and subnotebooks, a categorysometimes called ultralights.

Notebook Computer: A notebook computer is a portable computer thatweighs 4-9 pounds and is roughly the size of a thick notebook, perhaps81/2 by 11inches. Notebook PCs can easily be tucked into a /briefcase orbackpack or simply under your arm. Notebook computers can be just aspowerful as some desktop machines. Indeed, we are now at the pointwhere a notebook may fulfill just about all the needs of a desktop.

Subnotebook Computer: A subnotebook computer weighs 1.8-4 pounds.To save weight, subnotebooks in the past have often had external hard-disk drives, which were available as separate units.


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Pocket PCs: Pocket personal computers, or handhelds, weigh about1pound or so and can Ht in a jacket pocket. These PCs are useful inspecific situations, as when a driver of a package-delivery truck must feedhourly status reports to company headquarters. Another use allows policeofficers to check out suspicious car license numbers against a database ina central computer. Other pocket PCs have more general applications as

electronic diaries and pocket organizers.

In general, pocket PCs may be classified into three types:

(a) Electronic organizers are specialized pocket computersthat mainly store appointments, addresses, and "to do"lists. Recent versions feature wireless links to othercomputers for data transfer.

(b) Palmtop computers are PCs that are small enough tohold in one hand and operate with the other.

(c) Pen computers lack a keyboard or mouse but allowyou to input data by writing directly on the screenwith a stylus, or pen. Pen computers are useful forinventory control, as when a store clerk has to countmerchandise; for package-delivery drivers who mustget electronic signatures as proof of delivery; and formore general purposes, like those of electronicorganizers and PDAs.

Personal digital assistants (PDAs), or personal communicators,

PDAs are small, pen-controlled, handheld computers that, in their mostdeveloped form, can do two-way wireless messaging.


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Microcomputers w o r k s t a t i o n s

Two recent developments have altered the differences between workstations and PCs:

(1) Decline in workstation prices: A workstation that not long ago cost $15,000 or more is now available startingat $3,700, which certainly puts it within range of many PC buyers.

(2) Increase in PC power: In 1993 Intel introduced the Pentium chip; in 1994 Motorola (with IBM and Appleintroduced its PowerPC chip. Both of these very powerful microprocessors and their successors are nowfound in PCs. In addition, Microsoft introduced Windows NT, the first operating system designed to takeadvantage of more powerful microprocessors.

M I N I C O M P U T E R S / M I D R A N G E C O M P U T E R S

M A I N F R A M E S

The large computers called mainframes are the oldest category of computer system.The word "mainframe" probably comes from the metal frames, housed in cabinets, onwhich manufacturers mounted the computer's electronic circuits.

Occupying specifically wired, air-conditioned rooms and capable of great processingspeeds and data storage, mainframes traditionally have been water- or air-cooledcomputers that are about the size of a Jeep and that range in price from $50,000 to $5

million. Such machines are typically operated by, professional programmers andtechnicians in a centrally managed department within a large company. Examples ofsuch companies are banks, insurance companies, and airlines, which handle millionsof transactions.

Although mainframe manufacturers will probably promote new uses for their equipment, there appear to be threetrends:

(1) Old mainframes will be kept for some purposes.(2) Networks of smaller computers will grow.(3) Mainframes are being reinvented.

Workstations look like desktop PCs but are far more powerful. Traditionally,workstations were sophisticated machines that fit on a desk, cost many thousands ofdollars, and were used mainly by engineers and scientists for technical purposes.However, workstations have long been used for computer-aided design and

manufacturing, software development, and scientific modeling. Workstations havecaught the eye of the public mainly for their graphics capabilities, such as those usedto breathe three-dimensional life into movies such as Jurassic Park, Toy Story, andTwister.

Minicomputers are machines midway in cost and capability betweenmicrocomputers and mainframes. They can be used as single-userworkstations. When used in a system tied by network to several hundredterminals for many users they are known as midrange computers. Theminicomputer overlaps with other categories of computers. A low-endminicomputer may be about as powerful as a high-end microcomputer and costabout the same. A high-end minicomputer may equal a low-end mainframe.

Traditionally, microcomputers have been used to serve the needs of medium-size companies or of departments within larger companies, often for accounting

or design and manufacturing (CAD/CAM). Now many minicomputers arc beingreplaced by groups of PCs and workstations in networks.


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S U P E R C O M P U T E R S

BASED ON NUMBER OF USERS

Single-User Single user mode is a mode in which a multiuser computer operating system boots into a singlesuperuser. It is mainly used for maintenance of multi-user environments such as network servers. Some tasks mayrequire exclusive access to shared resources, for example running fsck on a network share. This mode may also beused for security purposes - network services are not run, eliminating the possibility of outside interference. Onsome systems a lost superuser password can be changed by switching to single user mode, but not asking for thepassword in such circumstances is viewed as a security vulnerability.

Multi-User - Multi-user is a term that defines an operating system or application software that allows concurrenaccess by multiple users of a computer. Time-sharing systems are multi-user systems. Most batch processingsystems for mainframe computers may also be considered "multi-user", to avoid leaving the CPU idle while it waitsfor I/O operations to complete. However, the term "multitasking" is more common in this context.

An example is a Unix server where multiple remote users have access (such as via Secure Shell) to the Unix shellprompt at the same time. Another example uses multiple X Window sessions spread across multiple terminalspowered by a single machine - this is an example of the use of thin client.

Management systems are implicitly designed to be used by multiple users, typically one system administrator ormore and an end-user community.

The complementary term, single-user, is most commonly used when talking about an operating system being usableonly by one person at a time, or in reference to a single-user software license agreement. Multi-user operatingsystems such as Unix sometimes have a single user process available for emergency maintenance.

ELEMENTS/COMPONENTS OF COMPUTERS

The various elements of computer are presented in Fig.1.1 below:

Typically priced from $225,000 to over $30 million, supercomputers are high-capacity machines that require special air-conditioned rooms and are the fastestcalculating devices ever invented.

Supercomputer users are those who need to model complex phenomena.Examples are automotive engineers who simulate cars crashing into walls andairplane designers who simulate air flowing over an airplane wing. "Supers," asthey are called, are also used for oil exploration and weather forecasting. Inaddition, they can help managers in department-store chains decide what to buyand where to stock it. Finally, they have been used to help redesign parachutes,which are surprisingly complex from the standpoint of aerodynamics. Thesupercomputer simulates the flow of air in and around the parachute during itsdescent. The most powerful computer, Janus, located at the Sandia NationalLaboratories in Albuquerque, New Mexico, and built by Intel, enables scientists tosimulate the explosion of a nuclear bomb.


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CENTRAL PROCESSING UNIT (CPU)

CPU is the most important component of a computer. It typically consists of a control unit, arithmetic and logical unitand a primary storage. It IS the brain of a computer and all processing takes place in the CPU. The functions of thecomponents of CPU are as follows:


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1. Primary Memory A memory or store is required in a computer to store programs and the data processed byprograms. The main memory, or primary memory, is made up of a large number of cells with each cell capable ofstoring one bit. The cells may be organized as a set of addressable words, each word storing a string of bits. Themain memory provides random access. Main memory is divided into Random Access Memory (RAM) and ReadOnly Memory (ROM). RAM is dynamic and volatile. ROM is read only memory and this memory cannot be erasedand rewritten, that IS, ROM is non-volatile.

2. Arithmetic Logic Unit (ALU) ALU does all the arithmetic and logical operations. Arithmetical operations involvemanipulation of numerical data such as addition, subtraction, division and multiplication.

Logical operations compare relative magnitudes of any two numeric, alphabetic or alphanumeric data items such asgreater than, less than, and equal to.

3. Control Unit (CU) Control unit controls and co-ordinates all the operations of the CPU and peripheral devicesIt ensures that the program instructions are carried out in the desired sequence and controls and co-ordinates theflow of data between the CPU and the input-output devices.

Modern computers operate on stored program concept. The control unit is designed to execute the stored programIts tasks are:

(a) Fetch the stored instruction whose address is in a special storage area called the Instruction Address Registe(IAR),

(b) Decode the instruction, that is, what operation is to be carried out and what data is to be used in the operation(c) Replace the address with that of the next stored instruction in IAR


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(d) Send signals to the rest of the system to ensure that the indicated operation is carried out. For example, for aninput or output operation, the CU would activate the I/O device and memory causing proper transfer of data.

(e) The above operations of the CU form a cycle and starts from step1 over again.

Computer Storage

Computer storage can be divided into primary storage and secondary storage. Primary storage or main memory in

the computer provides very fast access storage. Frequently used files and programs are stored in the primarymemory. Since primary storage is expensive, only a limited amount can be stored therein. But it can improve speedof processing as the CPU can access it faster than if data and instructions are stored on secondary storage devicesThe secondary storage is used for bulk storage of data and instructions. Large files and databases are stored onsecondary storage devices. These are then loaded on to the main memory in small measures for the CPU to accessfor processing.

Magnetic core technology and semiconductor technology have been used to make the main memory of computer.Today, semiconductor technology is widely used for it. The main memory is made up of memory cells. Each of themcan store one bit of data. This memory consists of electronic components called semiconductor chips. Each chipcontains several hundred thousand transistors; each transistor represents the binary state of a bit; on or off. Since abit can store only one value either l' or 0, bits are grouped into sets of eight bits called bytes. One byte can store onecharacter of data. Memory locations are numbered 0, 1, 2, 3,.etc. The unique number assigned to each location iscalled its address.

Memory is measured in terms of kilobytes (KB) (that is, 210 or 1024 bytes, roughly taken as 1000 bytes) andmegabytes (MB) (that is, 220 or roughly 1,000,000 bytes). Gigabytes (1024 MB) and Terabytes (1024 GB) are othestorage measures.

The main memory of a computer is measured mainly in terms of two characteristics viz., capacity and speed ofaccess.


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Primary Storage The primary storage or main memory is used to store data and instructions currently required foprocessing. Main memory can be divided into Random Access Memory (RAM) and Read Only Memory (ROM).These memories are manufactured by using integrated electronic circuits. Both RAM and ROM are random accessmemories and both can be used for reading purposes. The distinguishing feature is RAM's ability to alter data storedin it, which is not possible with ROM. Typically ROM, is used to store system instructions which are relativelypermanent in nature. RAM is volatile; that is, it loses its contents if the device is electrically disconnected.

RAM describes the way computers store and retrieves data and instructions from memory. It means that theprocess has direct access to each memory cell. Once the address of the location is given the processor can writeone character in that location or read one out from it into memory without reference to other cells in the memory.

Contents of some memory chips cannot be modified or rewritten. These memory chips are used to store data andinstructions that are relatively permanent. This memory is called Read Only Memory and is used to store programsthat are essential for the proper operations of computer system. ROM is non-volatile. Many computers especiallymicrocomputers come equipped with ROM chips that contain the operating system and application programsPrograms stored in ROM chips are often called firmware; that is, software built into the hardware.

RAM (Random Access Memory) The word 'random' means that the computer can access any memory celwithout accessing all cells sequentially. That is a memory is said to be random access memory if any part of it canbe accessed directly (randomly) for reading or writing data in the same time irrespective of its location. In otherwords, access to this memory is independent of physical storage location of information on the medium RAM isvolatile as any interruption in power supply results in loss of data in RAM The contents of the memory remain thereas long as electrical current is available to sustain the memory's pattern of positive and negative charges whichrepresent the two bits 1 and O. If power falls, all the contents in the memory will be lost.

ROM (Read-Only Memory) This memory uses Metal Oxide Semiconductor Technology. RAM is read-writememory whereas ROM is Read-Only-Memory. This memory is used to store frequently used programs in thesystem. ROM can be further divided into PROM EPROM and EEPROM.


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RAM and ROM In case of RAM it is possible to randomly select and use any location of this memory. Eachmemory location can be as easily and speedily accessed as any other location in memory, that is, it takes the sameaccess time wherever the location in the memory. It is possible to read from and write into this memory and hencethis memory is also called read/ write memory.

A Read-Only-Memory is one in which information is permanently stored. This memory cannot be written into. It canonly be read. When power is switched off, the contents of ROM remain unchanged. The manufacturers supply ROM

chips along with the programs therein. A variation of ROM chip is PROM. The PROM can be programmed to recordinformation using a special facility known as PROM programmer.

But once it is programmed using this facility, it becomes a ROM. PROM is also non-volatile. However there isanother type of memory chip called EPROM, which can be reprogrammed several times. It is possible to eraseinformation stored in EPROM chip by exposing it to ultraviolet light and reprogram It using a special PROMprogrammer facility.

PROM Programmable Read Only Memory can be programmed once. Special circuitry is used for programming itOnce programmed, this becomes read only memory.

EPROM Erasable Programmable Read-Only-Memory can be erased repeatedly and reprogrammed by the userErasing is done by exposing EPROM to ultraviolet light a specific frequency. Reprogramming requires speciaEPROM Programmer kit.

EEPROM Electrically Erasable Programmable Read-Only-Memory can be erase electrically and reprogrammedrepeatedly.

Cache Memory - I/O operations are very slow. CPU speeds are quite high compared to the access time of mainmemory; thus, the processor performance is limited by the slow speed of the main memory. To speed up fetching oinstructions to CPU, a buffer or cache (pronounced as cash) is used. Normal RAM is expensive and is not fastenough to match the speed of CPU. To reduce the processing time, certain computers use costlier and higherspeed memory devices to form a buffer or cache. This technique uses a small memory with extremely fast accessspeed close to the processing speed of the CPU. This memory is called cache and it stores data and instructionscurrently required for processing. Cache memory thus makes main memory appears much faster and larger than it

really is. It improves the memory transfer rates and thus raises the processor speed.

The CPU searches cache before it searches main memory for data and instructions. Cache is physically locatedclose to the CPU and hence access to cache is faster than to any other memory. Often used instructions are kept inthis c3che to speed up the fetching of instructions. Some processors use the cache as a work area also fortemporary storage of intermediate results.

Restricted use of cache memory can increase processing substantially without increasing cost significantly. Cachememory is in two forms: L1 and L2. One is built into the new microprocessor chip and the other is placed close tothe CPU so that it can access it faster and more efficiently. This high-speed memory increases the speed ofprocessing by making data and programs available to CPU at a rapid rate.


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COMPUTER SYSTEM

A computer system is made up of three major components: the hardware, software and the humanware. Thephysical units of a computer system excluding the third component constitute its hardware. Hardware consists ofmechanical, electrical and electronic parts of the system. Sets of programmed instructions constitute the software.Humanware is the people element in the system.

1. HARDWARE A computer, like a human brain, receives data and instructions, stores them and processes thedata according to the instructions given to it. It receives data from input devices, stores them in memory anddisplays them through an output device.

The physical devices that make up a computer are referred to as hardware. The computer hardware can be broadlyclassified into two: CPU and peripherals. The CPU is perhaps the most important part of a computer. The othehardware pieces like input devices, output devices, etc. are called peripherals.

a. Central Processing Unit (CPU) The CPU is the brain of a computer. It has an arithmetic logic uni(ALU) to perform arithmetical and logical operations. It has a control unit to co-ordinate the activities of theCPU and main memory for primary storage.

b. Peripherals They are usually the electromechanical devices connected to the CPU. They normallyexchange data and programs with CPU. The peripherals directly connected to the CPU are called on-linedevices, and devices not connected to CPU are called off-line peripheral devices. These peripherals can befurther divided into input devices, output devices and secondary storage devices.

2. SOFTWARE Software contains detailed instructions to the computer to perform tasks. It can be classified intosystem software and application software.

3. HUMANWARE Computer is only a tool. People use it for meeting their computing and communication needsThe people element of computer system includes personnel for data preparation and data entry, systems

analysts, systems designers, systems managers, information users in organizations etc.


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PERIPHERALS The input/output and storage devices surround the central processing unit (CPU). Hence they arecalled the peripheral devices. They are usually the electromechanical devices connected to the CPU that exchangedata and programs with the CPU. The users interact with the CPU through these devices. Thus, they act asinterface between users and the CPU. The interaction is difficult because of the language barrier. The CPU usesmachine language, which is difficult for most users. The I/O devices help in taking the translated version of the inputto the machine's memory and similarly, to render the processed symbols into the language of the user.

During the first two decades of commercial use of computers, I/O operation was performed mostly by punchingholes on cards and paper tape with a special device.

More direct and convenient I/O devices have been developed since then. The peripherals connected directly to theCPU are called online devices and devices not directly connected are called offline devices. These peripherals canbe further divided into input devices, output devices and secondary storage devices.

INPUT DEVICES Input devices allow the user to input data and instructions to the computer. There are a varietyof input devices. Direct entry of data generally requires a keyboard. It may also use other devices for direct dataentry like a touch sensitive screen, voice entry system and scanners.

Keyboard

Keyboard is the most popular input device for direct entry of data and instructionsinto the computer. It is linked to the CPU and is also linked to the computer screenso that the data entered into the memory can be seen by the user as he types in thedata.


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Mouse

A mouse is a small hand-held 'point and click' device that is connected to the CPUthrough a cable. It has a trackball at its bottom. It can be rolled across a flat andsmooth surface to control the position of the cursor on the screen. By pointing andclicking on icons and menu options displayed on the screen, it is easy for the user to

control the computer with a mouse.

Light Pen

Light pen consists of a stylus connected by a cable to the computer terminal. When thestylus is brought into contact with the screen, a dot appears there on the screen. Bymoving the stylus on the screen, lines and curves can be drawn on the screen that canbe stored and used as input.

Trackball

Trackball was originally built into the keyboard. Running a hand over the trackballmade the cursor on the screen to move. The cursor is used to make selection from amenu displayed on the computer screen.


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Joystick

Joystick is a small vertical stick attached to a trackball for easier mechanical movements. Itis used mainly in game programs.

Optical Mark Reader (OMR)

Optical mark reader (OMR) reads the presence or absence of amark on a paper optically. Light is directed on to the paper and thereflected light is analyzed for the detection of a mark. If a mark isthere on the surface of the paper, that area sends back lesser lightback to the OMR. It is used to read multiple choice answers in a testand the data are transferred to a computer for processing.

Barcode Reader

Barcode is a set of small bars of varying thickness and spacing printed on thepackages of products, on the back cover-pages of books, tags etc. The barcodereader uses an optical scanner to read product code and converts it into electricalpulses. The device is connected to a computer and the information read is passed tothe computer in digital form for automatic bill generation and updating of files. Thus,it is a direct data entry device as it obviates the need for an operator to key in saletransaction data.

Scanners

Scanners are direct-entry input devices. As the data entry is automatic, the scannersensure more accurate data entry. These scanners include optical scanners andmagnetic ink character readers. The optical scanners use light for sensing input andthey include OCR, OMR and Barcode reader.

Optical Character Reader (OCR)

Optical character reader (OCR) detects shape, and can identify characters canexamine each character as if it were made up of a collection of minute spots

Once the whole character has been scanned, the pattern detected is matchedagain a set of patterns stored in the computer. The pattern that matches ornearly matches is taken to be the character read. Patterns that cannot beidentified are rejected. It is used in mail sorting and credit card billing.


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Magnetic Ink Character Recognition (MICR)

Magnetic Ink Character Recognition (MICR) uses highly stylized character shapesprinted in a special ink containing particles that can be magnetized. This ink induces acurrent in a reading circuit, which is proportional to the area of ink being scanned. Thepatterns of the varying currents can be compared with and selected as bit patterns ofthe selected number e.g., the number on a cheque). The MICR reader can only identify

characters and cannot verify which has to be done manually. Banking industry uses thisdevice for sorting of cheques. The MICR codes read from the cheques are transmittedto an online computer for sorting.

Voice Recognition Systems

A special microphone is used to capture voice input. It converts the voice intoelectrical pulses and then into digital signals for onward transmission to acomputer for processing. A voice recognition system is provided with digital

patterns of a limited vocabulary of words and phrases. The system operatingin a training mode learns to recognize voice patterns by comparing thespoken input with the stored digital patterns. After identifying the input, thevoice system generates appropriate code for the machine to accept input andoperate. Voice recognition systems have enormous application in wordprocessing. A manager can directly dictate letters and notes to a wordprocessor through a speech recognition system. Similarly, the system canaccept oral commands and execute them. These systems are yet to becomepopular.

Tag Reader

Retail clothing units use a tag reader system. Clothes have price tags with datacoded on card tags. The tag reader decodes it and passes the data into thecomputer connected to it for billing and file updating.

Camera & Microphone

Most cameras like this are used during live conversations. The camera transmits a picturefrom one computer to another, or can be used to record a short video.

A microphone is used to record sound. The sound is then saved as a sound file on thecomputer.

Point-of-Sale Terminal (POS terminal)

The POS terminal consists of a numeric keypad and a few control or function keys. Theoperator at the point of sale counter enters the product code and quantity purchased bya customer. The terminal generates bill and, if connected to a computer, the systemupdates the related files automatically.


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Digital Cameras

Digital cameras are used to capture images and they can record the images onreusable floppy disks. Images are used with a digitizer for input to the computer. Oncethe image input is stored in computer, the image can be used in any application.

Vision Systems

A computer can be equipped with sensors to 'see' objects around. Robots with visionsystems are used in industrial engineering. They are used in complex operations likeassembling components requiring great precision.

OUTPUT DEVICES The output device displays output from computer processing for the user. The popular outpudevices are discussed in the section below.

Graphics Tablet

This is a flat surface input device, which is attached to the computer like a mouse. Itssurface is pressure sensitive. A special pen is used against the surface of the tabletand the cursor moves in response to the movements of the pen on the tablet. Thisinput device is particularly useful for graphic artists.

Visual Display Unit or Monitor

Visual display units (VDUs) are television-like screens that provide the user interface inthe form of display of text, numbers and images. The VDUs may be monochrome orcolor. The support of monochrome or color and clarity of display depend on the type ofvideo monitor and the video adapter installed in the microcomputer.

The video display terminal (VDT) consists of a monitor or CRT and a keyboard. TheCRT serves as an output device and the keyboard as an input device. Thus VDT is aninput-output device. If the terminal is provided with some memory and certainprocessing capability, it becomes a smart or intelligent terminal. A terminal withoutprocessing power is called a dumb terminal.


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Printers

Printers are purely output devices. They produce hard copy output. Computerprinters vary widely in their technologies and capabilities. They can beclassified in a number of ways. First, they can be classified into three broadgroups: character printers, line printers and page printers.

The character printers print one character at a time. Dot matrix printer (DMP), daisy wheel printer, thermal printeand inkjet printer are the various types of character printers. Drum printer and chain printer are line printers. Laserprinter and magnetic, printer are page printers.

They can also be classified into impact and non-impact printers based on the basis of the printing mechanism. Theimpact printing technology uses some mechanical pressure to produce images on paper. The impact printersinclude dot matrix printers, daisy wheel printer and chain printer. It is possible to take multiple copies of output with

Speakers

Modern computers using the appropriate software can turn text in a document into audiblespeech. This is known as speech synthesis. Other types of software allow music and other

sounds to be created and played back. The line between the computer and a homeentertainment system is becoming blurred. Computers are able to play music directly from aCD or play a film from a DVD. You can even fit your computer with a radio or TV card to addthese functions. In all cases, the sound is transmitted through a speaker in the same way itis in a sound system or radio.

Audio Response Systems

The computer can produce verbal output where the output or response can be standardized

as replies to special requests for information. The unit analyses the input and delivers theverbal reply by assembling the responses from pre-recorded words and phrases.


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impact printers. Non-impact printers do not use mechanical force to produce output on paper and hence canproduce only single copy output. Thermal printer, Inkjet printer and laser printer are non-impact printers. Of theseseveral types of printers dot matrix printer, inkjet printer and laser printer are very poplar.

Dot Matrix Printer

DMP is the cheapest in terms of operating cost. It prints one character at a time as a

set of dots produced by the pins on the print head. It uses a nine or twenty-four pinprint head. The pins or printing wires are aligned into the shape of the character tobe printed before the print head strikes the ribbon. The impact of the strike producescharacter shapes on paper. The speed of DMP is measured in character per second(CPS). A normal dot matrix printer with nine or twenty-four pin print head canproduce output ranging from 50 to 600 characters per second. It produces a lot ofnoise when working. The popular DMPs are Epson, Panasonic, Citizen, TVSE andLexmark.

Laser Printer

These are high-end printers. They are more expensive than inkjet printers and theiroperating costs are also higher than inkjet printers. They use the same technology asthat of Xerox copier machines and can produce both character and graphic output. Theygive the best quality output. Though expensive, they are becoming increasingly popular.

Thermal Printer

The thermal printer generates heat to produce the required character shape onspecially coated thermal paper. The print head, which carries electric current, burns thealuminum coating on the paper into the character form. It is a quiet printer.

Inkjet Printer

Inkjet is a non-impact printer and is quite when working. It sprays ink particles through

its nozzle. On leaving the nozzle, the tiny particles of ink get electrically charged. Theelectrically charged particles are then guided on to the paper to form appropriatecharacters. Low-end inkjet printers are cheaper than dot matrix printers; but theiroperating costs are higher than those of dot matrix printers. However, they give muchbetter quality than DMPs. They are available in black and white and color. Thepopular brands of inkjet printers are Hewlett-Packard, Epson Stylus and Canon.

Daisy Wheel Printer

The daisy wheel printer has a wheel with a number of spokes made up of metaland plastic. Each spoke carries a typeface at the outer end. The wheel rotatesuntil the appropriate character comes under the hammer, which strikes to producethe impression on paper. These wheels are inexpensive and removable. It is slowand produces noise like dot matrix printer; but it gives fine quality output.


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Drum Printer

It is a line printer. It has a drum that rotates at high speed. A set of characters isembossed on the drum. It prints one line of characters at a time. The hammer for aparticular character position is activated when that character on the drum passes

under it to produce character impression on paper.

Magnetic Printer

In a magnetic printer, a drum coated with magnetic material captures the imageof the page to be printed. These magnetic spots attract dry Ink particles, whichare then pressurized and transferred to paper to produce output.

SECONDARY STORAGE DEVICES Computer storage or memory can be of two types: primary and secondary

Primary memory provides very fast access and is used for storing frequently used programs and data. But, primarystorage is expensive and also volatile. Hence It used for storing data and instructions mostly temporarily. Large filesand databases are stored on secondary storage devices. Data and instructions from the secondary storage aremoved into the primary memory for the CPU to access them.

Secondary storage is thus supplementary to primary storage. It has larger storage capacity and is cheaper thanprimary storage. But access to secondary storage is slower than that to primary storage. Hence, secondary storageholds data and program not currently in use

Chain Printer

The chain printer works like the drum printer. It consists of a set oftypefaces Oil a chain that rotates at high speed. The printer composes oneline at a time and the hammers are activated to produce one row ofcharacters as it is composed. There is a hammer for each print position. Asthe characters move around on the chain, the hammer strikes on the

opposite side of the print position to produce character impression onpaper.

Graphic Plotters

Plotters are used for plotting graphs and designs on paper. Architects anddesigners use plotters to produce blueprints of their designs on paper. It is aspecial is output device for preparing computer drawn charts and graphs. !hemost popular type of plotter is the flat bed device. It plots on paper (or othermaterial) that is spread on flat bed.


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The secondary storage devices may be serial access or direct access device Magnetic tape is a serial accessdevice whereas magnetic disk and floppy diskettes are direct access storage devices (DASD). In serial accessstorage, retrieving a data element from a storage location requires going through the earlier records right from thebeginning of the file. On the other hand, direct access storage device stores ea data element in a storage locationwith a specific storage address that can individually accessed without referring to other data elements in storage.

A revolution is taking place in data storage technologies. As the storage devices are getting smaller and smaller, the

storage capacity is getting larger and larger. The popular secondary storage devices are magnetic disk, magnetictape and CD-ROM Important secondary storage devices are explained below.

Magnetic Disks

Magnetic disks are made of rigid metals or synthetic plastic material. The disk platter iscoated on both the surfaces with magnetic material and both the surfaces can be usedfor storage. The magnetic disk provides direct access and is popular for both small andlarge computer systems. The magnetic disk comes in two forms: floppy disks and harddisks.

Floppy Diskettes

These diskettes, made of synthetic plastic material, are flexible. Hence they arecalled floppy diskettes or simply floppies. Floppies are cheaper and more ruggedthan metal disks. The floppies were introduced in the early 1970s and became verypopular with the arrival of microcomputers. The floppies are popularly used onmicrocomputers. They are reliable and portable. They are available in many sizeslike 5 - inches and 3 - inches and vary in storage capacity from 360 KB to 2.88MB. The 5 - inch floppies are rarely used these days. The 3 - inch floppies,called microfloppies, can hold 1.44 MB to 2.88 MB of storage. The current trend istowards reducing the size and increasing the storage capacity of storage devices.With the arrival of flash memory devices, floppy disks are rarely used these days.

Hard Disks

Hard disk is a metal platter with magnetic coating on both sides. Several such hard disksare stacked one on the other, without touching each other, into a disk pack for largestorage. The disk pack, housed in metal container with a read/write head assembly unit,is fixed inside a computer permanently. Hard disks are highly reliable and accessing datafrom hard disk is faster and more efficient than that from floppies.

A disk pack is a collection of disks stacked vertically one on the other and it is mounted on a disk drive. The diskdrive has a head assembly with a read/write arm for each pair of recording surfaces. Each disk has two surfaces forstorage. The top surface of the first disk and the lower surface of the last disk are not used for recording as smalldust particles might settle down on them. The disk drive mechanism rotates the disk pack at a {constant speed.Each read/write arm has one pair of read/write head, one for each surface. To increase the speed of access, theread/write arm carries as many heads as the number of tracks on the disk.

The access time is determined by two factors: the seek time and the rotational delay. The seek time is the timerequired to locate the track on the recording surface.

Rotational delay involves positioning the read/write arm at the right track of the surface for reading/writing.


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Advantages of HD

They support direct access. They have quick access rates. They have fairly large storage capacities (20-MB storage to 7.5 GB storage Hard disks are essential for online systems.

Disadvantages of HD

Hard disks are expensive. Not always reliable. Speed and performance of hard disks is slower than that of CPU

Magnetic Tape

Magnetic tape is serial access storage medium. It can store large volume data at lowcosts. The conventional magnetic tape is in reels of up to 36~0 feet m3 of Mylar plastictape; the tape is one half inch in width and is coated with magnetic material on one side.The reel of tape is loaded on a magnetic tape drive unit. During any read/write operation;the tape is moved from one spool to another in the same way as in the audiocassette taperecorder.


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The conventional tape is replaced by cartridge tape that is housed in a small box that is cartridge, which is moreconvenient to use. This eliminates the need manually handle and thread the tape for any read/write operation. Themagnetic tape is densely packed with magnetic spots in frames across its width. A frame records one byte and eachbit in the frame is read/write head for that bit position. The tape has nine tracks, out of which eight are used as datatracks and the ninth one for parity bit meant for error detection.

The head assembly, with one head for each track, simultaneously reads from or writes bit streams on to the tape.

One track is used only for parity, which will be a bit with a value of either a 0 or 1 depending on parity conventionfollowed. In case of even parity, the number of 1s in the frame will be even. If the number of 1s in the data tracks isodd, the parity bit will be 1 so that total number of 1s in that frame is even. For example, if the data tracks carry thebits 00011100, then the parity bit is 1, that makes the total number of 1s in the nine bit stream an even number thatis four in the above example. If the parity is odd, the value of parity bit will be 0 so that the total number of 1s in theframe is odd.

Tapes are ideally suited for large storage for serial processing of data. They are generally used for backing up largevolumes of data required for serial processing. They are low-cost and reliable storage devices. They can store fairlylarge volume of data and are ideal for batch processing applications, storing historical data and backing up oimportant files.

It is also a cheap and effective secondary storage medium for ensuring security of data by backing up data andkeeping them off the site. Besides tape formats are more standardized than disk formats that facilitate transfer ofdata between machines. It can rapidly transfer data to the CPU. The disadvantage is that it permits only serialaccess and hence not suitable for many applications requiring direct access.

Differences between Magnetic Tapes and Magnetic Disks

1. Magnetic tape supports only serial access. Magnetic disk permits serial and random access.

2. Magnetic tape has much larger storage capacity than a magnetic disk.3. Magnetic tape is divided length wise into tracks and data are recorded in tracks. In case of disk it is dividedinto circular tracks and sectors. Data are recorded in one 3clctor fully before moving into the next.

4. Magnetic tape takes much more processing time than magnetic disk, as the access is serial.5. Accessing and updating of online disk files are much faster than tape files.6. A number of disk files affected by a single transaction can be updated simultaneously whereas tape files

have to be updated separately.7. Disk file updating process rewrites the old records, and data files have to be backed up for security.8. Disk storage is costlier than tape storage.


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CD-ROM

Compact-disk Read Only Memory is the most exciting development that has takenplace in secondary storage in recent years. CD-ROM can store huge quantity ofdata, over 650 MS, which is equivalent to 200,000 pages of ordinary text on a singledisk. It is relatively inexpensive and is used in both small and large computersystems.

This disk is made of synthetic resin that is coated with a reflective material, usually aluminum. When high intensitylaser beam is focused on the disk, it forms tiny pits on it. The pit represents I and the data are read using lowintensity laser beams. The pit reflects less intense light. The reflected light is sensed to know the bit o from 1; thelight will be more intense in the case of the former as there is no pit.

A special feature of CD-ROM is its ability to store different kinds of data such as text, pictures, animation, soundvideo and graphics. This makes it valuable for certain industries like travel, entertainment and motion pictures.

The data stored on CD-ROM is read only as the name indicates, that is, the data on CD-ROM cannot be modifiedHence it is well suited for storing relatively static data. Erasable and re-usable CD-ROM is also available now.

USB Flash Drive

It is a lash memory device with a universal serial bus (USB) connector. It is aremovable and rewritable memory device and is much shorter than a floppydisk. Its storage capacity ranges from 64 M8 to 32 GB or more. USB flashdrives have some advantages over other portable storage devices. They aremore compact, faster, hold much more data, are more reliable for lack ofmoving parts, and have a more durable design. All computers now have USBports. Some of them do not have floppy disk drives. Hence, USB flash drivesare becoming very popular as a portable storage device.

DVD

Digital Versatile Disc or Digital Video Disc is popular disc storage medium.DVD discs have the same diameter (120mm) and thickness (1.2mm) as aCompact Disc. But they have large storage capacity. A single DVD disc canstore up to 13 times the data contained on a CD, on one side. If both sides of adisc are used for data storage, it can store 26 times the capacity of a CompactDisc. Since it can store huge quantity of data, it comes handy for multimediaapplications. It is also used to store learning and training videos, movies andother home entertainment. The picture quality of DVD is very high andconsistent, that is, repeated play of the DVD gives the same picture quality forlong.


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COMPACT DISK

CD CD ROM CD-R CD-RW

CD (Compact Disc) an

optical digital audio discthat contains up to 74minutes of hi-fi stereosound. Introduced in theU.S. in 1983, the disc is aplastic platter(120mm/4.75" diameter)recorded on one side, withindividual tracks playable inany sequence. Its storagecapacity is from 650MB to700MB. Other forms ofCDs, such as CD-ROM,CD-I and Video CD, allstem from the originalCompact Disc-Digital Audio(CD-DA) format. CDs canbe played in CD, CD-ROM,CD-R, CD-RW and mostDVD drives.

Sound is converted intodigital code by sampling thesound waves 44,056 timesper second and converting

each sample into a 16-bitnumber. It requiresapproximately 1.5 millionbits of storage for eachsecond of stereo sound.The audio tracks arerecorded as microscopicpits in a groove that startsat the center of the disc andspirals outward to the edge.

CD-ROM (Compact Disc

Read Only Memory) Acompact disc format usedto store programs and datafiles. Holding either 650 MBor 700MB, the CD-ROMuses a different format forrecording data than theaudio CD (CD-DA), fromwhich it evolved. In the1990s, the CD-ROM rapidlyreplaced the floppy disk forsoftware distribution.

An audio CD player cannotread CD-ROMs, but CD-ROM drives can play audiodiscs. In a PC, most internalCD-ROM drives connect tothe ATA interface on themotherboard, althoughearlier drives attached viaSCSI. External drivesconnect via USB.

A CD ROM uses optical

technology. When data iswritten, small pits areburned into the surfaceusing a highly focused laserbeam. These are read byanother laser beam.

CD-R (CD-Recordable) A

writable CD technologyusing a type of compactdisc that can be recorded,but not erased (CD-Rs are"write once" discs). CD-Rdiscs are used to masterCD-ROMs, to back up dataand to make copies of datafor distribution. "Burning" aCD-R requires a CD-Rdrive, CD-RW drive or acombo CD/DVD drive. CD-R discs can be read onmost every type of CDdrive, including older CD-ROM units.

CD-RW (CD-ReWritable

The only rewritable CDtechnology. CD-RW diskslook like other CD mediabut with close inspectionthey have a morepolished surface with avery dark blue-gray castSimilar to a hard diskfiles can be added anddeleted, and the mediamust be formatted beforeuse. However, unlike ahard disk platter, whichcan be rewritten millionsof times, CD-RWs have amaximum limit of 1,000rewrites.

Note: In practice, the term "CD" refers to CD formats. The phrase "insert the installation CD" really means "insert

the installation CD-ROM."


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Documents

Fundamentals of Cs[1]