Computer fundamentals

Shree M. & N. Virani Science College

Computer
Fundamentals
By Milan Kothari

“Yogidham”, Kalawad Road, Rajkot – 5 Ph : 2576681 1


COMPUTER CONCEPT

Need for Computer literacy

Invention of computers has brought a major technological revolution. Computers have moved into society so
rapidly and so completely that we need basic computer skills to pursue our career goals and function effectively
in society. In short, to live and work in a computerized society we should be computer literate.

A mere knowledge of pressing the keys of keyboard and feeding data into the system is not only the objective of
being a computer literate. We need to understand some fundamental concepts about how computer systems
work and can be effectively used for general-purpose and special-purpose.

It is important to know how to handle a computer system otherwise one cannot take the full advantage of the
computers. Lack of knowledge causes several problems while using computers. Sometimes many people
generate irrational fear of computers and this is termed as cyberphobia.

Computer:

It is an electronic device or a flexible machine, which can manipulate data. These manipulations may or may not
be mathematical. Or more accurately a computer may be defined as a device that operates upon data.

Data can be anything like bio-data of various applicants when the computer is used for recruiting personnel. or
the marks obtained by candidates in a competitive exams such as medical entrance, engineering entrance, civil
service examination etc.

Data comes in various shapes depending upon the type of computer application. A computer can store. process
and retrieve data as and when required. Due to the fact that computers process data is so fundamental that
many people have started calling it a data processor.

Computers are so flexible that people feel comfortable and equally at home while using them. A computer is
programmable. It means computer depends upon the program which is in use by it. No matter which program a
computer is using, the machine-itself performs only four basic operations.

(a) Input: A computer accepts data that is provided by means of an input device. such as a keyboard, mouse,

scanner, smart card etc.

(b) Processing: A computer performs operations on the data and transforms it in some way.

(c) Output: A computer gives an output on a device. such as a printer, a monitor or a plotter.

(d) Storage: A computer stores the results of processing operations for future use, such as floppy disk. hard disk,

optical disk, cartridge tape.

Characteristics of computer:

The important factors that lead a person to use a computer are:

Speed.

Accuracy

Storage



Versatility

Diligence

Reliability

Memory capability.

Speed:

Computers are very fast. They can process millions of instructions per second. Computers can perform in
minutes, tasks that would take a person year to complete. Today, computers can perform 1000 million
computations in I second. The speed of computer is closely related to the amount of data it processes. The
terms used to describe the amount of data handled by a computer svstem are volume and frequency. Volume
represents the overall quantity of data and frequency describes how often a specific data item is used in
processing. Railway or Airline reservation system illustrates frequency.

Accuracy:

Computers are accurate. They do not make mistakes in calculations. The probability of computer error is quite
small and often traceable to faulty data. Computer can perform all

kinds of complex calculations -accurately. The degree of accuracy of computers depends upon their design.
But, for a particular computer, each and every calculation is performed with the same accuracy. Errors in
computers are not of technological nature but are mostly due imprecise thinking of the programmer. The main
examples in front of us are:

(a) Space shuttles
(b) Nuclear simulation reactions.

Storage:

Computers are having enormous storage capacity. Computers can store a vast amount of information, which
can be recalled at any time in fraction of seconds. The information is stored in the form of files, but on disks and
tapes. This helps in easy and speedy retrieval of information. This storage is known as electronic storage
system. This system removes the duplication of information being stored. For example, in a company or an
organization the details of employees are given such as name. address. basic salary, unique code number etc.,
that may be required by accounts department as well as personnel department. In case, an employee resigns or
is promoted, then the updation of the information is required only once and at one place. Now a days standard
storage capacity of a computer is in the range of 20 GB- I 00 GB.

Versatility:

This is one of the most wonderful things about the computer. Computers can do a variety of jobs depending
upon the instructions fed to them and their hardware characteristics. Modern computers can be used in
railways. air reservations systems, process controls, nuclear reactors. manufacturing plants, scientific
laboratories, hospitals and hotels etc. They can also act as controlling devices in children toys. Briefly, a
computer is capable of performing any task provided that the task can be reduced to a series of logical steps.
Their versatility can further be demonstrated by their use in cleaning the streets of a city, improving the existing
sewage system to landing man on mars.

Diligence:

Computers are diligent in nature as they can perform complicated and respective tasks very well with full
concentration. without committing any error, for long periods of time. Computers do not suffer from
carelessness, boredom or tiredness. Moreover. their efficiency does not decrease with age. If millions of


calculations are to be made with exactlv the same accuracy even then computer will not show any tiredness and
commit any error.

Reliability:

Computer systems are widely accepted due to their exceptional reliability. Unlike huma beings they are capable
of operating under the most adverse conditions for extended period of time without showing any sign of fatigue.
They do not take sick days and coffee breaks Computers are very reliable. We can consider them as very
faithful super servants o humanity.

Memory Capability:

Computer systems have the capability to recall the total data instantly and an almost unlimited capacity to store
this data. A typical mainframe computer can have billions o characters and thousands of graphic images stored
and available for instant recall.

The above characteristics of computers enhance human capabilities of doing analytical work at high speed.

It is important to mention that in spite of all wonderful characteristic of computers they had certain drawbacks.
They have no I.Q. They have no feelings and cannot work like human beings.

Advantages of Computer:

Computers are having advantages over other computing devices as they are fast, reliable, accurate, can store
massive amounts of information, can move information quickly from one place to another and are versatile in
nature.

The advantages of computers can be listed out as below-
(a) Perform repetitive tasks.

(b) Are more accurate while dealing with large numbers.
(c) Work at constant efficiency.
(d) Are used in almost every field.
(e) Process millions of instructions in a fraction of a second.
(f) Are effective and efficient data storage and retrieval.

After having looked at the characteristics of a computer, the advantages of using it become very obvious. These
are:

(a) The speed at which the computer carries out its operations.

(b) It's versatility, i.e. can be used in different fields.

(c) Enable an individual or an organization to store and retrieve information as and when required.

(d) Feeding of information is required only once in one Organization or company and the same can be used by
different departments of the Organization of company.

(e) Instant recall of information is possible. Any format of reports can be taken about individuals, group of
individuals etc.

Limitations of computers:

(a) Non-affordability: The high cost of installation of computers puts a limit over its use. However, due to
the advent of PCs and super mini-computers and mini super computers, a common man can also afford to buy a
computer.


(b) Compatibility: Programs and software written for one type of computer or microprocessor cannot be
used for other type of microprocessors.

(c) Dependent upon human beings.

(d) Have no imagination and intuition of their own.

(e) Tasks have to be described in detail.

(f) Cannot detect flaw or error in logic.

(g) Need of an expert programmer: Today a large number of computer languages are in use
and also there are lots of operating systems. Complete knowledge of system software (operating system)
along with application software is a must. Computers process data in a step-by-step fashion according to
the programs written for it. If any mistake occurs in programming, then an error is bound to occur in
processing the data, which leads to wrong calculations in the output.

(h) Unlike the human brain, a computer cannot think on its own, but has to be imparted instructions in a very
explicit manner to perform a task. Even, instructions have to be given to prepare the reports as desired by the
user.

(i) There is a lack of creativity and imagination. It does not have any advantage of its experience of
working on the same program or different programs. Every task is new to it because it follows the instruction of
the program.

0) Non-standardization: A large number of versions are available and to use a given hardware and
software it is essential to have their complete knowledge of compatibility. No sincere efforts have been made so
far to standardize the various software and hardware.

Applications of Computers:

Today, computers have their utility in almost every sphere of life - particularly in the areas where calculations are
done at very fast speed. Computers now a day are being used in almost every department to do the work at a
greater speed and accuracy. They can keep the record of all the employees and prepare their salary bill in a
matter of minutes. They can also keep checks on the stock of a particular item. Big commercial houses and
companies use software packages to control and monitor their production system, dispatch system. account
system and many more. These packages need high level of expertise to develop, use and maintain. These
packages cost huge amount of money.
These days computers can be used for followings:

(a) Materials Management

(b) Production planning and control
(c) Purchase
(d) Credit and collection

(e) Warehousing

(f) Marketing information systems

(g) Manufacturing information systems

(h) Multimedia

(i) Science and technology

j) Banks are using special software packages for monitoring their working. At any point of time the
concerned authority can have details of cash deposits, cheque deposits, overdrafts, interest charges on the loan
amount etc., in a matter of minutes. -



(k) Schools are using special software packages for fee administration, finance, transport, time scheduling,
and payroll Record of students, Performance of teachers.

In future, computers will find extensive use in the areas of

Information networks

Communications

Artificial intelligence

Parallel processing

Biochips
Voice recognition

Robots

Negative effects of Computers

(a) Computers may pose a threat to personal privacy, because every kind of data of a person can easily be
Stored and recalled.

(b) Computer manufacturing processes require the use of hazardous chemicals, which could endanger human
lives.

(c) Too much use of computer can result in painful nerve injuries, such as carpel tunnel syndrome.

(d) In case of computer failures in a critical system, such as air traffic control system, lives may be
endangered.

(e) Computers may displace workers by automating tasks that people use to perform. Since computers work
more efficiently and effectively therefore. fewer numbers of workers may be required in place of large
Number. The displaced workers may lose their salary substantially il'at all they get ajob.

Elements of Computer

It is necessary to know the architecture i.e., the internal structure of a computer to understand the functioning of
a computer.

"A computer, as we have learnt, is an electronic device which accepts instructions and data, stores it as long as
required, processes the given data according to the instructions (programs) given to it and gives the output as
and when required".

If we analyze the above information, we find computer system to essentially perform the following functions:

(a) Accepts the information (Input).

(b) Manipulates the information (Processing).

(c) Stores the information (Storage).

(d) Displays the result (Output).

This definition is often referred to as IPOS cycle.


Equipment and program are two essential parts of a working computer system. In computer terminology, all
computer programs are known as software and all computer peripherals are called hardware.

HARDWARE

The term hardware refers to the physical parts of the computer. Computer hardware is versatile and it depends
upon the computer program you use.

Hardware is a general term use to represent the physical and the tangible components of the computer itself i.e.,
those components. which can be seen and touched. It includes

Input devices.

Output devices.

Memory.

Processor.

Storage devices.

The electronic circuits consisting of resistors, capacitors, ICs etc., inside a computer are all examples of
computer hardware. All input and output devices connected to the computer are collectively known as
peripherals.

Add-ons are boards containing chips and printed circuits which are inserted into slots on the main system board
for the purpose of adding memory, graphics capabilities, co-processors, or other capabilities to the computer.

The key to computer's versatility is memory. We can think of memory as a temporary workspace. The
computer's processor uses this workspace during processing. Memory is temporary and storage is usually
permanent. On most computers, storage has far greater capacity than memory. To describe large capacities,
the terms kilobyte (KB), megabyte (MB), and gigabyte (GB) are used. One byte equals only one character.

Input Devices:

These are the devices bv means of which data are entered into the computer system. The most common input
devices are:

(a) Kev board

(Data entered of the keyboard is directly sent to the CPU. There is no intermediate step.)

(b) Mouse

(It is a pointing device. It is used to link keyboard to communicate with the computer.)

(e) Readers of punched lards

(These type of devices were very common in the, earlier years. Now keyboards are used.)
(d) Paper and magnetic tapes

(The data is first accepted from the keyboard and stored on magnetic tapes. From these tapes the data
is sent to CPU.)

(e) Light pen

(This is used for drawing on the screen.)



(f) Joystick

(This is normally used for playing computer games.)

(g) Optical image scanners

(It uses optical technology to capture the image from the image provided to it.)

(h) MICR (Magnetic Ink Character Recognition)

(It uses special ink to print characters which can be read and decoded by special magnetic devices. This
system is widely used by banks for processing cheques.)

(i) OCR (Optical Character Recognition)

(A scanner converts the image that it sees into numeric digits before storing the image in the computer.
This conversion proves is known as digitising.)

OMR (Optical Mark Reader)

OMR uses optical technology to detect the presence or absence of mark in standard position on a form.)

(k) Audio sensors.

(Input in the form of sound waves sent to CPU)

(m) Temperature sensors.

(Temperature is measured and sent to CPU)

Output Devices:

These are the devices, which translate processed data from a machine-coded form to a form that can be read
and used by people.

When processing is complete in the CPU, the information produced is stored in the memory in a computer
understandable format. This information has to be transcribed into a form that can be read by the user, which is
achieved by output devices.

There are two types of outputs produced by output devices:

(i) Soft copy: An output on the VDU or stored on magnetic media such as magnetic disks and tapes.

(ii) Hard copy: An output produced on a printer or a plotter,

The most common type of output devices are:

(a) Monitors

(Monochrome or black and white, colour).

(b) Printers


(Different types of printers are used with personal computers and they are classified by the method of printing.
Mainly there are three types of printers connected to personal computers.
Dot Matrix Printer, Ink Jet Printer, Laser Printer

(c) Graphics plotters

(a plotter is a device used for producing outputs such as blue prints etc. for example, flatbed plotters, drum
plotters. Plotters come in different sizes such as A-4, A-2, A-1 etc.)

A new type of output device used now-a-days is speech synthesizer; a software attached to the computer that
produces verbal output sounding like human speech.

Memory:

Memory is electronic holding place for instructions and data that your computer's microprocessor can reach
quickly. When your computer system is in normal operation, its memory usually contains the main parts of the
operating and some or all of the application programs and related data in use.

Memory is often used as a shorter synonym for random access memory (RAM). The primary memory section of
memory is a part of CPU and usually consists of mixture of RAM and ROM. As secondary memory the
computer may also have floppy disks, magnetic hard disk, or laser optical disks.

Memory has two purposes.

(a) To store the binary codes for the sequence of instructions to be carried out by the computer according to
the program written.

(b) To store the binary-coded data with which the computer is going to be working. For example, inventory
record of a company or a market.

Processor.

It is also referred as the brain of the system. It is that part of the process the data which contains electronic
circuit to process the data. Depending on the instructions of input devices it performs operations on the data. It
also controls the flow of data through the system, directing the data to enter the system, placing it in memory and
retrieving it when required and directing the output.

The CPU consists of

(a) ALU (Arithmetical Logic Unit): It takes logical decision and performs all type of arithmetical calculations.

(b) Memory - It is the unit where all data, intermediate and final, are stored. The data from an input unit are
transmitted to computer memory unit where they are available for processing. This unit also holds the
instructions for processing of data.

(c) Control unit - It controls all the activities of other units of computer system. It receives instructions from
memory unit. It decodes these instructions. It decides the routing and store of these instructions.

Storage Devices:
Many people confuse memory with storage. Memory is temporary. Everything in memory is lost when you turn
off the computer. Storage is usually permanent. Almost on all the computer systems, storage has far great or
capacity than memory.

Most common storage devices are categorized as:

(i) Primary storage devices.


(a) RAM (Random Access Memory)
(b) ROM (Read Only Memory)

(ii) Secondary storage devices.
(a) Floppy disk.
(b) Hard disks.
(c) Optical disks.
(d) Cartridge tape.
(e) Spool tape.

SOF'TWARE:

The non-tangible components of computer system are, referred to as software.

Software consists of the instructions to be passed to computer to perform the desired functions. Sequential
instructions, which direct the system to perform a specific task is called a program. Making of these sequential
instructions is termed -as programming. Programs may be simple or complicated based on number of
instructions.

Computer software can be broadly classified into three categories:

(a) System software:
Software, which has its orientation more towards the operation of the hardware components of the computer
system i.e., concerned primarily with coordinating and controlling hardware resources.
Or,
It is an integrated set of specialized programs that is used to manage the overall operations of a computer.

The term system software is generally used to describe program that make computer more adaptable and easy
to use. The system software makes available to the programmer all facilities that might be useful to develop
programs.

The examples of system software are:

Operating systems.

Assemblers, Compilers, Interpreters.

Programming aids.

Report generation.

Telecommunication programs.

Utility or service programs.

Editors.

For example, DOS, Windows498, Windows-NT, Unix, Linux etc.

(b) Utility software:

The software, which has its orientation more towards facilitating the use of computer and the various application
software, is called utility software.

For example, calendar, calculator, software to manage data stored on the disk, etc.


These are the programs used to perform specific talks like duplication,copying etc.

(e) Application software:

The application software are created for specific use. They are not common usage programs. These are the
programs, which direct the computer to perform a specific task as desired by a user, such as printing of mailing
list, printing of payroll of employees. These programs are available in the. Areas of business, education,
manufacturing applications, desktop publishing, designing, graphics and web browsing.

They provide flexibility. We can modify and' change the programs . when requirements change. Normally
source codes for application programs are available for modification.

Application programs are written in higher level programming languages such as COBOL, C++, VISUAL BASIC,
JAVA etc.

INPUT/OUTPUT DEVICES

Computers are known for their speed and accuracy. But to do some work i.e., to process it requires some data.
Raw data is to be given to the computer which is expected to be converted into information after process- In
short, the working of the computer can be understood as any machine, which requires some input, processes it
and produces the output. Graphically it may be understood as:

Input Devices

To process, the computers need raw data. This raw data is to be input to the computers using certtain devices
known as input devices. Today, a large number of input devices are available in the market suiting our various
requirements.

Input devices transfer data into a computerized information system so that it can be reused. Remember, that the
computer does not process information it processes data.

Here are two different categories of input devices:

(a) Manual Input Devices:
With a manual input device the user must enter data into the computer by hand e.g. mouse, keyboard, scanner
etc.

(b) Direct Data Entry Devices:

Direct data entry device can transfer information automatically from a source document ---- as form or barcode
into the computer. The user does not need to manually enter the information e.g., optical mark recognition etc.

This device resembles a typewriter and is today the most widely used device to input information in the form of
words and numbers. This layout of keys is called QNWRTY because Q-W-E-R-T-Y is the order in which the
letters occur on the top row of the keyboard. Like typewriter keyboard contains alphabetic, numeric and special
characters. Unlike typewriter, which records the data on the paper, each character keyed in, using keyboard is
encoded into the computer system's data coding scheme and is stored in computer's memory.

Along with normal expected keys the special keys include, Control, Shift, Alt, Return, Escape, Arrow keys and
Function keys (Fl to F10 or F12).

Applications make use of the keys according to their requirement.

For example,



F2 is used by many applications to save data permanently.

Fl is frequently used to provide context sensitive help to the users.

Page Up, Page Down, Home and End keys are used for cursor movements.

Caps Lock is used to type in capital letters.

Num Lock is used to toggle the use of numeric keypad available on the keyboard.
Shift keys can also be used to type in uppercase or lowercase according to the on or off of the Caps Lock key.

Pointing Devices

When the interface is graphical one easier way of selection and feeding information to system is the pointing
device. Various pointing devices available are:

The mouse and Track ball

Mouse comes in sizes slightly bigger than Indian Match box. It rolls over bearing. When the user rolls the mouse
across a flat surface, such as desk, the screen cursor moves in the direction of the mouse's movement. It
becomes very easy in the graphical environment like that of Windows to move, cut, copy, paste or open files and
folders using this pointing device.

Tracker ball is something similar to the mouse but less complicated and designed for use by ".children. This has
got a spherical ball, which can be rotated by fingers in various directions to affect screen movements.

Touch Pad

· is a small device, which can be embedded directly into various systems like laptops and -,books. Pointing
devices like mouse does not find place with such devices because they mainly used for mobile computing. A
separate device for input does not match the idea for compact and lesser space. The user can move his finger
on the touch pad surface and .Luc input just like the mouse.

Joystick

Joystick resembles a stick and is used as input device, specially, in game and multimedia software. The type of
input from this device mainly comprises of the movement of cursor on the screen or movement of screen output
in various game software.

The best joysticks, called analogue joysticks measure how far the joystick is being moved in the direction it is
being pulled. This information is used to set how quickly the object on the screen moves. The further you push
the joystick the faster the object moves.

Small joysticks, called track-point devices, are sometimes built into the keyboards of portable computers and
used instead of mouse.

Touch sensitive screens

Small touch sensitive boxes are provided on the screen of the monitor itself, which act something like the
function keys present on the keyboard. The idea is to dispense with the keyboard and allow data to be input by
touching the screen with the fingertip or other unit provided for the same purpose. This form of input is
particularly suitable to applications design for use by the general public, for example, searching library catalogue
files. Though it is very user friendly but a large amount of data cannot be input using this device and only the


functions like selection and pointing can be done. Touch screens are not used very often, as they are not very
accurate, tiring to use for a long period and are more expensive alternatives like a mouse.

Pen based systems.

Light pen is another pointing device similar to any normal pen and can be used effectively to input data.
Proper software can be used to input data in users own handwriting and can be also useful for graphical work,
for example, the user at a computer aided design (CAD) terminal can draw directly on the screen with the pen.

Data scanning devices

There may be need that the input is not to be given in words or numbers but through are available data typed on
a page. Various available data scanning devices can be used to scan and input data through available
documents. Various available data scanning devices include:

Optical recognition systems

(a) Barcode reader (BCR) scans a set of vertical bars of different widths for specific data and are used to read
tags and merchandise in stores, medical records, library books etc. It is a direct data entry device.

Barcodes are often printed on products that we buy and are used to produce bills for customers. The number is
often printed above or below the bar code so that humans can read it.

Barcodes are read into computer using a moving or a fixed scanner. Barcodes are not easily damaged and can
normally still be read if they are creased or not stuck onto a flat surface. They can be printed using a normal
printer and ink and so are cheap to produce. The information normally included on bar code for a product is
country of origin, manufacturer and item code. The price is not included in the bar code.

(b) Optical mark reader (OMR) this device is used mainly to recognize marks made by pencil or pen. The
device can be used in various competitive exams where the method of examination is objective type and
the candidates are required to fill the answer sheets with pencils. For such type of exams pre-printed
answer sheets with containing boxes or squares for correct answers are used. The candidates are
required to fill the desired box or square with lead pencil.

The reader detects where the marks are placed by shining a light at the page and measuring the amount of light
reflected. Less light is reflected where the marks have been made.

Input using OMR is accurate and very fast. Problems can occur if the OMR forms get creased as the-reader
may jam.

(c) Optical scanners can be used to scan images, posters, magazine pages, other physical objects like
ornaments etc., and can be directly stored into computers memory. This device is particularly useful for
multimedia producers who need to input large amounts of printed historical text and turn it into searchable
data.

The optical sensor reads information about one line of the image at a time. They must be moved down the
picture to input the whole image. There are two different types of scanner:

(i) Flatbed Scanner: You place the image on top of the scanner. The scanner moves the light and
sensor itself and scans the whole image automatically. Most flatbed scanners are A4 size.

(ii)Handheld Scanner: You must manually push the light/sensor along the image. Handheld scanners
are usually 5 inches wide.


Flatbed scanners are better as they can scan larger images and are more accurate than handheld scanners. On
the other hand, handheld scanners are cheaper and more portable. The price of flatbed scanners has fallen so
much in- recent years that handheld scanners are rarely sold now.

Some other known input devices are as follows:

(d) Magnetic Ink Character Recognition (MICR)

The MICR system reads characters printed in special magnetic ink into the computer. The main users of MICR
are banks. They use it to read information from cheques into their computers so that the cheques can be
cashed. Here is some information stored on a cheque using MICR

The information printed on the cheque using MICR is

• A unique number for the cheque.

• A code that identifies the bank and branch that issued the cheque.

• The number of the account that the cheque relates to.

MICR readers can only read one special font, which can represent only numbers and a few punctuation marks.
They can read characters very quickly and with 100% accuracy. Information printed in magnetic ink is also very
secure. It is not possible to change the (information by writing over it with a pen, and the printed numbers are
not damaged by folding (as often happens with cheques). Both the reader used by NUCR and the special ink
are expensive.

(e) Optical Character Recognition (OCR)

An optical character recognition system consists of a scanner and some software. The scanner is used to scan
an image of a page of text to be read into the computer. The software examines the page and extracts the text
from it, storing it in a form that can be processed.

OCR systems can now recognize a wide variety of computer fonts and read letters with o 95% accuracy. Some
systems will recognize hand-written text reasonably well as long as it is written very neatly and usually put into
boxes on a pre-printed form.

Voice recognition systems

These devices can directly take input in the form of human voice and translate it in digital, form understandable
by the computers. The device finds its usage in modem offices where managers need to dictate letters and
other official documents and want to save time and stationary in first dictating the matter to write and then to
convert it to digital form through keyboard.

Voice recognition systems listen to what people are saying and carry out the instructions given to them when
people speak. A microphone is used to provide input for a voice recognition system. Currently, these systems
are not very sophisticated and are used only for certain applications. Existing voice recognition systems come in
two different types:

(a) Systems, which recognl2;e only a few words but can understand most peoples voices e.g. telephone
banking computers.

(b) Systems, which recognize a wide vocabulary but need to be trained to understand each different voice
e.g. automatic dictation systems.

In the last few years a number of voice dictation packages have been developed. packages let the user dictate
text into a computer to appear in a word processor' d Dictating like this can be much quicker than typing but the
computer still mat mistakes especially with short words.



Output devices.

The input data are to be processed and need to give certain output. The devices used to the output from the
computer are known as output devices. An output device takes data from the computer and converts this into
information in a form, which is normally understandable by humans. Various output devices available are:

Monitors

It is also known as video display units (VDU) or simply screen. This is the most widely used capacities and is
available in medium to view the output. it comes in various sizes and various modes for text and graphical
outputs

An image displayed on the screen is made up of lots of dots called pixels. If you look at the screen you may be
able to see these pixels. The resolution of the screen is "how many pixels there are up and down and from left
to right across the screen".

A variety of resolutions are available. For PC these resolutions have names e.g. VGA is 640 x 480. This means
there are 640 pixels in each row across the screen and 480 pixels in each column up and down the screen.

SVGA is usually 800 X.600. Displays with lots of pixels are called high resolution. Displays fewer pixels are
called low resolution. High-resolution display can show much more detail than low resolution ones and are
required for applications, such as Computer Aided Designing and Multimedia.

Cathode ray tube (CRT)

It resembles television and takes input from the CPU and displays data. It has separate storage of about I kg,.
capacity in the form of core or I.C. memory. The memory relieves the computer during display by storing the
data. The more sharper the image can be displayed, the unit is said to be having more resolution.

Flat panel monitors

These form the latest in display technology. it takes less power to move molecules than to energize a light-
emitting device like CRT. Flat screen monitors first used only in notebook computers a re fast invading the
desktop. The completely flat screens sharply reduce reflection from the users environment and eliminate glare.

Liquid Crystal Display:

Besides the displays discussed above, the latest in the field is the Liquid Crystal Display. These displays are
completely flat and so can be used in portable computers and other small devices such as calculators. They are
more expensive to make than desktop monitors. Currently, only the most expensive ones are as high quality as
desktop monitors. In ten years time LCDs will probably replace bulky desktop monitors.

Audio output

This unit permits the computer to talk back to us. This makes computer an excellent interactive medium to work
with. All the sounds needed to process the possible enquiries are pre-recorded on a storage media. Each
sound is given a. code when enquiries are received. The processor follows a set of rules to create a reply
message in coded form. This coded message is then transmitted to an audio response device, which
assembles the sound in the proper sequence and transmits the audio message back to the station requesting
the information.

On PCs you also need to install a Sound Card to be able to output sound. If you want you @can connect the
computer to a hi-fi to et louder, better quality sound than you would if you, plugged the loudspeakers straight into
the computer. The sound produced by PC-s is now of better quality than sound that is recorded on a CD.

With proper software a computer can read out text that has been printed into it by using a computerized or
recorded voice. This type, of system is known as speech synthesis.



Printers.

The hardcopy of the data stored in the computer's memory is taken through printers, which is also an output
device like VDU. Printers can also be classified according to their nature. These are needed to produce a hard
copy output. Unlike images on a screen hard copy can provide a permanent record of work and can be looked
at away ftom the computer. Hard copy can be obtained using a printer or a plotter. There are lots of different
types of printers and plotters available. They vary in the method they use to produce hard copy and the cost and
the quality of the hard copy they produce. Different devices are suitable, for different applications. Following is
the tree of printer family according to their classification:

Hard copy output device

Printer Plotter

Impact Non-Impact Flatbed Drum

Dot Matrix Daisy Wheel Line Laser Ink Jet Thermal

Printers can be divided into following categories:

Impact printers

The technology uses the direct mechanical contact between the print head and the paper. These use variations
of standard typewriter printing mechanism where hammer strikes paper through inked ribbon. Because of the
hammering action impact printers are noisy when they are printing. Various types include solid font and dot
matrix printer.

Daisy Wheel Printer
Daisy wheel printers are rarely used any more. A daisy wheel printer hammers character stamps (like those on
typewriters) against a ribbon to produce high quality text output. The character patterns are all arranged around
the edge of a wheel. When a letter is to be printed the wheel rotates so that the correct letter is against the
ribbon to print it on the paper. Daisy wheel printers are very slow and noisy. It is not possible to print graphics
using a daisy wheel printer.

Line Printers
Dot matrix and daisy wheel printers both print only one character at a time. For that reason they are called
Character Printers. In contrast a line printer prints a whole line (typically 80 or 132 characters) of text at a time.
These printers are very fast. They are expensive to buy and are used when high volumes of output are required.
Example applications include printing telephone bills or bank statements.

Non-impact printers:

These printers use technology where there is no direct contact between the print and paper giving longer life to
the print head. They print characters by spraying small drops of ink on to paper. Because there is no hammering
action non-impact printers are very quite but cannot print multiple copies using carbon paper. Examples include
inkjet, laser printer etc.

Laser Printer



Laser Printers are called Page Printers because they print a whole page at a time. A laser beam is used to draw
the image to be printed onto a light sensitive Drum. After the image has been drawn on the drum, fine powder
ink called Toner is put onto it. The toner only sticks where the laser has drawn the image. The paper then
passes over the drum and the toner is transferred onto the paper.

Laser printers produce very high quality output, are very quiet and very fast. Typical home laser printers can
print 8 pages per minute (ppm). Some industrial versions print over 40ppm and can print on both sides of a
piece of paper at the same time.-,,The main disadvantage of this type of printer is the high cost.

Inkjet Printers

Ink jet printers are the most popular t .Ype of printer for use at home or in a sma I business. This is because
they are relatively cheap to purchase and can print in colour. Ink jet printers generate output by squirting tiny
jets of ink at the paper to be printed on. A column of ink jets in the print head moves across the page squirting
dots onto the page to make the image. Typically ink jet printers can produce 360 or 720 dots per inch (dpi) but
these dots are larger than those that a laser printer makes so the quality, although very good, is not quite as
perfect. Ink-jet printers can work in black and white or colour.

STORAGE DEVICES

Storage devices are used to store every kind of data. The concept of data covers important business facts and
figures and various other official documents. Data is a backbone of any business and proper storage and
retrieval of data is a must.

Computers are known for their speed and accurate calculation capabilities but if the data is not saved properly,
then everything will be in vain. Thus, storage of data is an important concept and various technologies are
involved in this concept. Here -we will try to understand various technologies and devices capable of storing and
retrieving data.

The main points those should be kept in mind in terms of storing data are:

(i) Storage should be economical,

(ii) It should be secure and safe

(iii) Data storage device should be capable of storing almost unlimited amount of data.

Storage in computers is classified as two types

a. Internal

1. RAM

2. ROM

b. External

Where Internal storage is the computer's own storage, which is further classified into two types RAM and ROM.
On the other hand external storage is nothing but the external devices that has to be attached with computer in
order to have the data stored in it. External storage devices can be named as Floppy Disks and Compact Disk
etc.

Let us take the example of a Audio cassette player that plays a music cassette in it. When we play a audio
cassette in the Audio Cassette Player it is played and we are able to hear music on the speakers, but the


moment we take out the cassette the music is no more played. But on the other hand a computer will keep on
running the software on the screen even if the floppy disk is removed from the drive and kept outside. This is
because of the fact that the computer initially reads the information from a floppy disk and store it in RAM once it
is fully stored in RAM even if the disk is removed from the drive the software keeps on running. Hence RAM is
the most essential part of the computer. In simple language we can say that whatever we are viewing on the
screen is present in the RAM. RAM stands for Random Access Memory, which is temporary memory in itself. If
the computer is switched -off while on it, whatever is there in the RAM goes off and next time we have to reload
the entire thing. This is the reason we have to save the file we are working on.

On the other hand ROM stands for Read Only Memory, which is a permanent memory in it ROM is basically
storing the computer startup instructions in it. Whenever we switch on our computer it performs a self-check
because of ROM. Instruction in ROM are permanent i.e. once fed by the manufacturer of the computer and can
never be changed by the user. Software permanently embedded in Hardware is called as FIRM WARE.

Storage devices discussed here are also known as secondary, auxiliary or back up storage. Secondary storage
devices can be used to store programs and data in a machine-readable form for processing at a later date, or for
holding data on a temporary basis during the processing of a program. It provides a means of retaining
information on a permanent basis.

Besides providing space for retaining working file, secondary device may be used to retain copies of files. The
secondary storage is external to the CPU. A secondary device is therefore also a peripheral device, just as any
input or output device.

Various types of devices are available for data storage. These include:

Magnetic Storage Devices.
These devices use electromagnetic principles to store data. The devices normally take shape of circular disks.
Data are recorded on disk in concentric circular bands called tracks. The tracks on a disk are similar to the
grooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors. Two or more
sectors combine to form cluster.

Magnetic devices like -floppy disks, hard disks and some tape units all use the same underlying technology to
achieve this. The media (meaning the disk as opposed to the drive) is coated with magnetic particles a few
millionths of an inch thick, which the drive divides into microscopic areas called domains. Each domain acts like
a tiny magnet, with north and south poles, and represents either zero or one depending on which way it is
pointing.

Available devices of such type are:

Diskette drives:

Also known as floppy disks, it is 'a flexible circle of mylar plastic. It comes in two sizes viz. 5.25 inches and 3.5
inches in diameter respectively. 3.5 inches floppy are newer and capable of storing more data because of newer
technology used in such device, making 5.25 inches floppy drives nearly obsolete.

The density of magnetic particles on the disk's surface determines the amount of data that can be stored on a
floppy disk.

The head is moved by a lead-screw, which in turn is driven by a stepper motor; when tie motor and screw rotate
through a set angle, the head moves a fixed distance. The data density of floppies is therefore governed by the
accuracy of the stepper motor, which means 135 tracks per inch (tpi) for 1.44MB disks. A drive has four
sensors: disk motor; write-protect; disk present; and a track 00 sensor, which is basically an edge stop.


The magnetic head has a ferrite core, with the read/write head in the centre and an erase head core on either
side. The erase heads wipe out a strip either side of a new data track to avoid interference from old data tracks.
Bits are stored as magnetic inversions, the inversion intervals being two to four microseconds (µs). The read
signal goes to a peak detector and is processed to produce a binary signal by the electronics in the drive. This is
then sent back to the PC.

Floppy disk's head actually touches the diskette as a result both the media and the heads wear out early. Track
life for a diskette is generally on the order of 3 to 5 million contact revolutions.

Floppy comes in low density and high-density versions each affecting the amount of data that can be packed in
the single unit of the diskette.

Future of floppy disks:
The 200MB to 300MB range is best understood as super-floppy territory. This is about double the capacity of
the would-be floppy replacements with performance more. similar to a hard disk dm a floppy disk drive. Drives
in this group use either magnetic storage or magneto-optical technology. The magnetic media drives offer better
performance, but even MO (Magneto-optical drives, discussed later) drive performance, at least for the SCSI
versions, is good enough to allow video clips to be played directly from the drives.

Hard Disks:

It is made of rigid metallic platters and functionally works same as floppy disks. These are generally
permanently encased in the disk drive. These are capable of storing large amounts of data in range from 10 MB
to more than 20 GB (gigabytes). These disks drives can have four or more disk platters in sealed unit. In most
of these disk units the read/write head never touches the surfaces of the disks thus, giving more life to the disk
as compared to floppy disk where there is a mechanical touch between the disk and the read/write head.
Because of capable of storing huge amount of data and capability to read and write data at more speed these
are used widely in microcomputers.

When a disk undergoes a low-level format, it is divided it into tracks and sectors. The tracks are concentric
circles around the central spindle on either side of each platter. Tracks physically above each other on the
platters are grouped together into cylinders, which are then further subdivided into sectors of 512 bytes per
piece. The concept of cylinders is important, since cross-platter information in the same cylinder can be
accessed without having to move the heads. The sector is a disk's smallest accessible unit.

Drives use a technique called zoned-bit recording in which tracks on the outside of the disk contain more sectors
than those on the inside.

There's a read/write head for each side of each platter, mounted on arms, which can move them towards the
central spindle or towards the edge. The arms are moved by the head actuator, which contains a voice-coil - an
electromagnetic coil that can move a magnet very rapidly. Loudspeaker cones are vibrated using a similar
mechanism.

There are typically 3000 tracks on a platter side. Data is stored on both sides of the platter. Separate arms are
provided with read/write heads to read and store on these platters. The read/write head consists of tiny
electromagnetic. The shape of the head end acts like an airfoil, lifting the read/write head slightly above the
spinning disk below.

When the disk rotates under the read/write head. it can either read existing data or write new ones. If a current
is applied to the coil, the head will become magnetic. This magnetism will orient the micro magnets in the track.
This is write mode.

When the head moves along the track without current applied to the coil, it will sense the micro magnets in the
track. This magnetism will induce a current in the coil. These flashes of current represent the data on the disk.
This is read mode.

Removable hard disks:



Hard disk are encased in the disk drive. This makes the data transfer an issue of concern from one place to
another. The capacity of floppy disks is much less, so more data can't be transferred at a time. This generates
the need of removable hard disk that can store large amount of data as well the unit can be detached from the
computer system easily and could be relocated to another system easily.

Optical Storage devices:

These form the second category of storage devices. These are most advanced in terms of technology used.
These devices use optical (LASER) technology to access data. This makes the life of device high and more
reliable for data storage. The technology involves a high power laser beam to bum microscopic spots in disk's
surface coating.

Available devices using this technology are:

Compact Disk Read Only Memory (CD ROM)

The CDROM is a thin piece of clear polycarbonate plastic with a metal layer covered with a protective layer of
lacquer, with the aluminum layer measuring 120 mm in diameter. It is mostly useful in multimedia applications
where data is huge and needed to be transferred from one place to another and the requirement is of secure
data. The disk can also be used to distribute songs that also require huge amount of space and to distribute
bundled software packages. The main disadvantage of this type of media is that they are read-only that means
disk manufacture can only data on them and rest can only read from it. But this point is also a strong point in
favor of using them because this makes them safe against any kind of accidental or purposeful destruction of
data.

CDs measure 12cm in diameter with a 15mm diameter centre hole. The audio or computer data is stored from
radius 25mm (after the lead-in) to radius 58mm maximum where the lead-out starts. The Orange Book CD-R
standard basically splits the CD into two areas: the System Use Area (SUA) and the Information Area. While the
latter is a general storage space, the SUA acts much like the boot sector of a hard disk, taking up the first 4mm.
of the CD's surface. It tells the reader device what kind of information to expect and what format the data will be
in, and is itself divided into two parts: the Power Calibration Area (PCA) and the Program Memory Area (PMA).

CD-Recordable (CD-R), WORM and Photo CD

The disadvantage of CD ROM is removed by using what is known as WORM disk (Write Once Read Many).
This allows to write on disk at user's choice but once written the data cannot be altered later.

The characteristics of a CD-R were specified in the 0 range Book 11 standard in 1990 and Philips was first to
market with a CD-R product in mid-1993. It uses the same technology as WORM, changing the reflectivity of the
organic dye layer, which replaces the sheet of reflective aluminum in a normal CD disc. In its early days,
cyanine dye and its metal-stabilized derivatives were the de facto standard for CD-R media. Indeed, the Orange
Book, Part 11, referred to the recording characteristics of cyanine-based dyes in establishing CD-Recordable
standards.

Phthalocyanine dye is a newer dye that appears to be less sensitive to degradation from ordinary light such as
ultraviolet (UV), fluorescence and sunshine.

Also dye has been used in other optical recording media and is now also being used in CD-R.

These dyes are photosensitive organic compounds, similar to those used in making -photographs. The media
manufacturers use these different dyes in combination with dye L,4uckness, reflectivity thickness and material
and groove structure to fine tune their recording characteristics for a wide range of recording speeds, recording
power and media longevity. To recreate some of the properties of the aluminum used in standard CDs and to


protect the -d ye, a microscopic reflective layer-either a proprietary silvery alloy or 24-carat gold - is coated over
the dye.

el use of noble metal reflectors eliminates the risk of corrosion and oxidation. The CD-R media manufacturers
have performed extensive media longevity studies using industry .Red tests and mathematical modeling
techniques, with results claiming longevity from 70 op to over 200 years. Typically, however, they will claim an
estimated shelf life of between 5 and 10 years.

OPERATING SYSTEMS

The present day computer is perceived as a very fast and accurate electronic machine that is designed to
automatically accept, store input data, process it and produce output results under the directions of a stored
program of instructions.

The physical and tangible components of this machine are termed hardware and the sets of instructions stored
as programs that govem its operations and turn the h/w merchandise into a usable system is termed as
software.

Furthermore, the s/w part that contributes to control and performance of this system are categorized as system
s/w, mainly meant to recognize, synchronize and process inter-hardware communication.

The specific task or purpose oriented user programs like accounting, designing are categorized as application
software.

The physical resources of such a machine are the processor, main memory storage devices and 1/0 devices.

The fundamental part of system software, which primarily-controls, manages and provides a centralized access
to the machine resources, is the operating system. The operating system provides an interface or a virtual
machine. which keeps away user from the complex internal h/w functioning and acts as a basic platform for the
application programs to run.

Hence the information sciences see the functionality of the operating systems as

1. An extended or virtual machine provider

2. A resource manager

Examples of various modem operating systems are DOS, WINDOWS 95, WINDOWS98, UNIX, LINUX etc.

COMPUTER SYSTEM STRUCTURE

The computer system structure is based upon the various levels of functionality and interaction between a user
and the system machine intervals. The execution of the machine is alienated from the user by some bottom
layers. Levels of transparency between layers increase as we move from bottom to top layers. Based upon this,
the structure is divided into 6 layers with categorization into 3 basic levels:

6. HIGH LEVEL LANGUAGES, WORD PROCESSORS

[APPLICATION PROGRAMS]

-------------------------------------------------------------------------------------------

5. COMPILERS, EDITORS, INTERPRETERS

[SYSTEM PROGRAMS]
---------------------------------------------------------------------------------------------



4. OPERATING SYSTEM
[SYSTEM PROGRAMS]

---------------------------------------------------------------------------------------------

3. MACHINE LANGUAGE
[H/W]
----------------------------------------------------------------------------------------------

2. MICROPROGRAMS
[H/W]
---------------------------------------------------------------------------------------------

1. PHYSICAL DEVICES
[H/W]
--------------------------------------------------------------------------------------------

When a user works on a computer on any application e.g. DocumentProgramming language like C++, he writes
commands in English language in proper format and syntax. They are first checked and interpreted by
application programs specifically meant for the purpose e.g. compiler like a turbo C++ compiler. This
interpretation works using operating system like Win98/NT as a basic platform which further makes this
translated set of instructions available to the Machine and Machine in turn translates it into its own language
called Machine Language or the Binary Language. The final process involves making the tangible H/W
understand the language by the instructions implemented in the physical device itself by the manufacturer and
this instructions se t is called a micro-program e.g. system BIOS. The physical devices like HARD disk
drives/CD-ROM's respond as per the binary instructions.

The bottom 3 layers of the Devices, Micro-programs and Machine language are completely alienated from the
user so it is taken as part of H/W. The O/S and the compilers etc. provide management and control functions
with apparent levels of transparency between user and this virtual machine and are termed system programs.
The topmost layer, which directly interacts with the user, are termed application programs.

OPERATING SYSTEM CONCEPTS

A user of a computer system interacts directly with an application software program for his purposeful task. The
task works over a platform which is the O/S.

History & Evolution of Operating Systems

The history & evolution of operating systems can be viewed in relation to the history & evolution of computer
systems over the time. The computer system evolution has been broadly classified into four generations, which
also led to the development of operating systems as per need and demand of users.

1. ZEROETH GENERATION: MECHANICAL PARTS:

Charles Babbage, an English mathematician, designed the first digital computer using wheels, gear etc. But the
machine so developed was slow and unreliable.

2. FIRST GENERATION (1945-1955): VACUUM TUBES:

The mechanical design of earlier generation changed to electronic design using the vacuum tubes. The
machines thus formed were huge and generated lot of heat during running. Till this time switches were used to


feed a calculation for each word, the counter was set to the first word and a start button was pressed to get the
output in the form of lights and bulbs.

3. SECOND GENERATION (1955-1965): TRANSISTORS:

Around 1955 Transistors were introduced in the USA at AT&T. The machines using these transistors used
switches for feeding input and light and bulbs for output as before.

The entire operation of pressing several switches for each word was very time consuming.

The solutions developed for faster processing comprised of the following:
Step1
Reduce the loading time and human involvement-prepare an offline job card and feed it to the result.

For each calculation to be performed a different job card was needed to be prepared and loaded which was
again very time consuming because of repetitive switching On/Off of the computer system. The solution
proposed was that on start up itself a computer should read a loader program, which further loads another
complex program. The complex program was specially meant to process the job cards. Then assembly
language emerged and programmers jobs was simplified The job cards (batch processing systems) now were
substituted by assembly language programs. This entire process of switching on the machine and successive
loading of programs was called booting.

Step2

Improve the output and get textual results.

The monitors evolved to act as principal output device. Apart form the monitors the printers were also
developed.

Step3

Improve the input and feed textual entries.

The keyboards were developed which acted as principal input and the interface device the user and the
computer.

With the development of transistor technology faster processors were produced which could produce results
very quickly. The system processor however, remained idle for most of the time during input feeds.

Step4

Faster speed to cope up with faster processor.

Other hardware had to be modified for equivalent faster speeds giving rise to faster keyboards, 1/0 devices etc.
Faster disk drives were also developed.

In 1960 the first operating system oriented computer ATLAS was developed at Manchester University.

4. THIRD GENERATION (1965-1980): INTEGRATED CIRCUITS

IBM announced system/360 series of computers in 1964. The interrupts were developed. Single stream batch
processing changed to Batch multi-programming.


A series of jobs were loaded in one go, which were processed one by one by the processor. If the processor
needed to wait for input- output device response for a job it could in the meanwhile process another job. Thus
the concepts of foreground and background processes were developed.

IBM also provided utilities such as Simulators and Emulators to enable old software to be run on IBM 360 family
of computers. But it was found that operating system of large machine created problems When run on small
machines and also the operating system of small machine were ineffective on large machine So IBM delivered
four operating systems within same range of computers. These were

DOS/360 for the small 360 systems

OS/MFT for the medium 360 systems

OS/MVT for the bigger 360 systems

CP-67/CMS for the powerful 360/67, using virtual storage

Thus the concepts of family of computers and operating systems evolved.

The concept of spooling was developed during this period.

The concept of time-sharing and multi-programming (execution of many simultaneous programs) was enhanced
giving rise to another popular operating system called MULTICS (Multiplexed Information and Computing
Service). It was a joint effort of MIT, Bell Labs and General Electric. It served to create a computer utility which
could support hundreds of simultaneous time sharing users. Later on the name UNIX was adopted which is
popular till date.

The only problem with this system was that it was not portable for different architectures because it was written
in assembly language. Then a computer scientist Dennis Ritchie designed and implemented a high level
language called 'C' and rewrote whole of UNIX in 'C' language. The new system made an application written on
UNIX 90% portable after which the UNIX source code was made available to many Universities freely. Later
multi user versions of LNIX were developed.

5. FOURTH GENERATION (1980-1990): LARGE SCALE INTEGRATION:

With this technology thousands of transistors could be packaged on to a single chip. This helped in producing
different computer modules like Resistors, Adders, Multiplexers, Decoders and a variety of other digital circuits.
A new design of computers called as microcomputer evolved which was developed on Intel 8080 in 1974. This
design became popular because of its user friendliness.

After the advent of the IBM-PC based on Intel 8086 and then its subsequent models, the 'Disk Operating
System' (DOS) was written. Finally a company called Microsoft Corporation acquired the rights for QDOS( A
later version of DOS) and produced its operating system as MS-DOS. Later on with the development of 386,
486 and finally Pentium Processors, new operating systems based on Graphical User Interfaces (GUI's) have
been developed e.g. windows 3.11, Win95, Win98, WinNT etc. which are popular till date. WinNT/Novell
Netware like operating system are products meant for another type of computing called distributed processing
and serve as true Network Operating System. Newer operating systems are currently under development, which
will enhance multi-programming and powerful computing making the latest era of real-time computing and online
computing truly possible with the aid of marvel tool INTERNET.

Kinds of Operating Systems

Batch Processing Systems

In earlier computers, the users didn't interact directly with the system, instead, a user prepared a job, which
consisted of program, data, and some control information about the nature of the job and submitted it to the


computer operator. The operating system of such computer had the function to transfer the control from one job
to another. To speed up processing, jobs with similar needs were batched together and were run through the
computer a group. Thus, the programmers would leave their programs with the operator. The operator would
sort programs into batches with similar requirements and, as and when the computer became available, would
run each batch. The output from each job would be sent back to the appropriate programmer.

A batch operating system, thus, normally reads a stream of separate jobs, each with its own control cards that
predefine what the job does. When the job is complete, its output is usually printed. The definitive feature of a
batch system is the lack of interaction between the user the job while job is being executed. The job is prepared
and submitted and at some later time the output appears. The delay between job submission and job
completion may result from the amount of computing needed or from delays before the operating system starts
to process the job.

OPERATING SYSTEM

USER PROGRAM AREA

Memory layout for a simple batch system.

In this execution environment, the CPU is often idle. This idleness occurs because the speeds of the
mechanical I/O devices are intrinsically slower than those of electronic devices. Even a slow CPU works in the
microsecond range, with thousands of instructions executed per second. A fast card reader, on the other hand,
might read 1200 cards per minute. Thus, the difference in speed between the CPU and its I/0 devices may be
three orders of magnitude or more. Unfortunately, CPU speeds increased even faster, so that the problem was
not only unresolved, but also exacerbated.

Multitasking Systems

a. Multitasking (or TIME SHARING) is a logical extension of multiprogramming.

b. In Multitasking Multiple jobs are executed by the CPU switching between them. It is of two types

-> Pre-emptive multitasking
-> Co-operative multitasking

PRE-EMPTIVE MULTITASKING/NON PRE-EMPTIVE (CO-OPERATIVE)
CPU scheduling decisions may take place under the following 4 circumstances:

1. When a process switches from the running state to the waiting state, (for e.g. I/0 request or invocation of wait
for the termination of one of the child processes)

2. When a process switches from the running state to ready state (for e.g. when an interrupt occurs)

3. When a process switches from waiting state to the ready state (for e.g. completion of I/0)

4. When a process terminates.



When scheduling takes place only under circumstances 1 & 4, we say the scheduling scheme is non-preemptive
(co-operative) otherwise the scheduling scheme is preemptive.

Windows 3.11 operating system uses co-operative multi-tasking.

Windows 95 and later operating systems use preemptive multitasking.

TIME SHARING SYSTEMS

Time-sharing is a logical extension of multiprogramming. Multiple jobs are executed by the CPU switching
between them but the switching occur so frequently that the uses may interact with each program while it is
running.

Time sharing systems were designed to produce interactive use of computer systems at a reasonable cost. A
time-shared operating system uses CPU scheduling, and multiprogramming to provide each user with a small
portion of a time-shared computer. Each user has at least one separate program in memory, which is called a
process. When a process executes, it generally runs for only a short time before it either finishes or needs to
perform Since 1/0 typically takes place at human speed, which is incredibly slow as compared to the electronic
speed of the CPU, so the CPU is idle during the I/0 operation. Rather than let the CPU be idle, the operating
system will rapidly switch the CPU to the program code of the other user. As the system switches rapidly from
one user to another, each user feels as if the -@PU is dedicated to his program, whereas actually one CPU is
being shared among many users.

Real-Time Systems

A real time system is a special type of O/S and is used when fixed time-constraints for a processor response or
data output are defined. The system is used as a Control device in dedicated applications. If the system does
not produce the required result within the pre-defined time-constraints, it fails. Real-Time systems are sensor
controlled where in sensors provide data to the computer which is analyzed and controls are adjusted to modify
sensor inputs. e.g. Industrial Control Systems, Weapon Control Systems, ROBOTICS, automobile fuel injection
systems are real time

A real time system can be designed in two ways.

(a) As a Hard real time system, which is completely time bound. In this type o system support features like
Virtual Memory etc. are missing and processing takes place in non-volatile memory or the Read Only Memory
(ROM). This design differs from conventional OS design of time-sharing systems where H/W is separated from
user by distinct levels of S/W.

(b) As a Soft real time system which is like a time-sharing system. Here priorities are taken into consideration
for critical tasks to be completed but long waiting times are avoided. Since a soft real time system does not
operate in fixed time constraint so it is not used in critical applications like ROBOTICS or Industrial Control but is
used in applications like Multimedia Design and Virtual Reality. In these systems advanced O/S features like
Virtual Memory need to be provided. Some latest versions of Unix provide real time operation features.


Computer fundamentals

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