CATEGORIES OF SOFTWARE

 The computer being a machine cannot perform on its own. It needs to be instructed to
perform even a simple task like adding two numbers. Computers work on a set of instructions
called computer software (programs), which clearly specify the ways to carry out a task.
Software can be categorized as system software and application software. System
software is a generic term for referring to any computer program whose purpose is to help the
user to run the computer system, whereas application software employees the capabilities of a
computer directly to a task that the user wishes to perform.

SYSTEM SOFTWARE:

System software consists of several programs, which are directly responsible for
controlling, integrating, and managing the individual hardware components of a computer
system. You must have noticed that a new computer system is always accompanied by some

software, either stored in a floppy or CD, which is supplied by the manufacturer. This software
manages and supports the computer system and its information processing activities.
System software is more transparent and less noticed by the users, they usually interact
with the hardware or the applications this software provides a programming environment in
which programmers can create applications to accommodate their needs. This environment
provides functions that are not available at the hardware level and performs the tasks related to
the execution of an application program. Hence, system software acts as an interface between
the hardware of the computer and the software application.
In simple terms, system software makes the computer functional. They provide basic
functionality like file management, visual display, and keyboard input are used by application
software to accomplish these functions. Some examples of system software are:
1. Operating system
2. Device drivers
3. Language translators
4. System utilities.

1. Operating System:

It is the first layer of software loaded into computer memory when it starts up. As the
first software layer, all other software that gets loaded after it depends on it for various common
core services. These common core services include disk access, memory management, takes
scheduling, and user interfacing. In addition the operating system ensures that different
programs executing at the same time do not interfere with each other. It provides a software
platform on top of which other programs can run. In simple words, the operating system
organizes and controls the hardware. Examples of operating systems are Windows XP, UNIX,
and Linux. The basic functions of an operating systems are:
a) Process Management:
It handles the creation, deletion, suspension, resumption, and synchronization of process.
b) Memory Management:
It handles allocation and de-allocation of memory space as required by various programs.
c) File Management:
It is responsible for creation and deletion of files and directories. It also organizes, stores,
retrieves, names, and protects all the files.
d) Device Management:
It manages all the devices of the computer system such as printers and modems. If any
device fails, it detects the device failure and notifies the same to the user.
e) Security Management:
Protects system resources and information against destruction and unauthorized use.
f) User interface:

 Provides the interface between the user and the hardware.

2. Device Drivers:

Device drivers are system programs, which are responsible for proper functioning of
devices. Every device, whether it is a printer, monitor, mouse or keyboard, has a driver program
associated with it for its proper functioning. Whenever a new device is added to the computer
system, a new device driver must be installed before the device is used. A device driver is not an
independent program; it assists and is assisted by the operating system for the proper functioning
of the device.

3. Language translators:

Computers only understand a language consisting of 0s and 1s called machine language.
To ease the burden of programming entirely in 0s and 1s, special programming languages called
high-level programming languages were developed that resembled natural languages like
English. Language translators help in converting programming languages into machine
language. To be precise, they convert programming statements into the 0s and 1s that the
computer is able to process.

Depending on the programming language used, language translators are divided into
three major categories: compilers, interpreter, and assembler.
a) Compiler:
The programs written in any high-level programming language (C or Pascal) needs to be
converted into machine language. This is achieved by using a complier.
b) Interpreter:
An interpreter analyses and executes the source code in line-by-line manner, without
looking at the entire program. In other words, an interpreter translates a statement in a program
and executes the statement immediately, before translating the next source language statement.
c) Assembler:
Compared to all the types of programming languages, assembly language is closest to the
machine code. It is fundamentally a symbolic representation of machine code. The assembly
language program must be translated into machine code by a separate program called an
assembler. The assembler program recognizes the character strings that make up the symbolic
names of the various machine operations, and substitutes the required machine code for each
instruction. In short, an assembler converts the assembly codes into machine codes, making the
assembly program ready for execution.

Typical software generally comprises millions of lines of programming statements or
code. The code is divided into logical groups and stored in different independent modules so
that the debugging and maintenance of the code becomes easier. Before execution, different
object codes resulting from the independent modules have to be linked together to create and
executable program. A linker is a system program that links together several objects modules
and libraries to form a single, coherent, program (executable program). The part of the operating
system that brings an executable file residing on disk into memory and executes it is known as
loader. Being responsible for tasks like loading, linking and relocation, loader performs the
function of a linked program and then immediately schedules the executable for execution
without creating an executable file as an output.

4. System Utility:

System utility programs perform day-to-day tasks related to the maintenance of the
computer system. They are used to support, enhance, and secure existing programs and data in
the computer system. They are generally small programs, having specific tasks to perform:
a) File Management:
These utilities make it easier to manage data files. Many programs are written to help users
to find the files, create and organize directions, copy, move, and remove files.
b) Backup:
It may happen that sometime data files are corrupted, or accidentally deleted. In such a
case, data backups become very useful. A backup system utility is essential for those
organizations, which want to keep their data intact.
c) Data Recovery:
It is the process of retrieving deleted or inaccessible data from failed electronic storage
media such as computer hard disk drives, removable media, optical devices, and tape cartridges.
d) Virus Protection:
Anti-virus programs are essential system utilities for a computer system functioning in a
network. They provide the security to the system form viruses that can damage the computer
system.
e) Disk Management:
Disk management program includes various system softwares like disk defragmenter,
data compressor and disk formatting tools. De-fragmentation implies putting fragments of files
in a sequential order onto the disk which reduces the time to access the file.
f) Firewall:
It is commonly used to protect information such as e-mail and data files within a physical
building or organization. Essentially, a firewall is designed to protect a computer from
unauthorized access, especially via network.
g) Disk Cleanup:
To keep a computer running smoothly, regular maintenance is vital. Therefore, one
should use the disk cleanup utility, which easily determines which files on hard drive are no
longer needed, then delete those files.

APPLICATION SOFTWARE

The most often seen software by a user is the application software. It used to accomplish
specific tasks rather than just managing a computer system. For a user, the computer system has
no specific use without application software. Application software may consist of a single
program, such as Microsoft’s Note pad (for writing and editing simple text). It may also consist
of a collection of programs, often called a software package, which work together to accomplish
 a task, such as database management software. Application software may also include a larger
collection of related but independent programs and packages (a software suite), which have a
common user interface or shared data format, such as Microsoft Office suite.

Applications softwares are dependent on system softwares. A system software (like
operating system) acts as an interface between the user and the computer hardware, while
application software performs specific tasks. Applications are pieces of software that perform
tasks for the user besides helping the computer operate, which is the tasks of system software.
Applications softwares are controlled by system software, which manages hardware devices and
performs background tasks for them. The distinction between the two is important. Without
system software, the computer will not run, and without application software, the computer, no
matter how powerful, will not be helpful in meeting user requirements. Think of it this way applications apply the computer’s thinking power to business tasks such as tracking the general
ledger or billing your customers.

Application software ranges from games, calculators, and word processors (document
creating programs), to programs that “paint” images on screen (image editors). Applications
represent real world tasks. They can be easily divided by looking at exactly what function they
serve. Some of the most commonly used application software is discussed below:

1. Word processor:

A word processor is software used to compose, format, edit, and print electronic
documents. Word processing is one of the earliest applications for office productivity and the
personal computer. It involves not only typing, but also checking the spelling and grammar of
the text and arranging it correctly on the page. A variety of different typefaces is available for a
verity of effects. It is possible to include pictures, graphs, charts and many other things within
the text of the document. It also allows for changes in margins, fonts, and colour. Nowadays,
virtually all personal computers are equipped with a word processing program, which has the
same function as a typewriter for writing letters, reports or other documents, and printing.
Examples of some well-known word processors are Microsoft Word and Word Perfect.

2. Spreadsheets:

One of the first commercial uses of computers was in processing payroll and other
financial records, so the programs were designed to generate reports in the standard
“spreadsheet” format bookkeepers and accountants used. A spreadsheet application is a
rectangular grid, which allows text, numbers, and complex functions to be entered into a matrix
of thousands of individual cells. The spreadsheet provides sheets containing cells each of which
may contain text and / or numbers. Cells may also contain equations that calculate results from
data placed in other cells or series of cells. A simple example might be a column of numbers
totaled in a single cell containing an equation relating to that column.
Spreadsheet software are used predominantly for accounting a other numerically-based
tasks, because financial and mathematical data and analysis are often managed in a tabular style,
with columns of financial figures being manipulated and then influencing other data
computations. Microsoft Excel and Lotus 1-2-3 are examples of spreadsheet applications.

3. Image Editors:

Image editor programs are designed specifically for capturing, creating, editing, and
manipulating images. These graphics programs provide a variety of special features for creating
and altering images. In addition to offering a host of filters and image transformation
algorithms, some image editors also enable the user to create and superimpose layers. Most
graphic programs have the ability to import and export one or more graphic file formats. These
computer programs enable the user to adjust an image to improve its appearance. With image
editing software, one can darken or lighten an image, rotate it, adjust it contrast, crop out
extraneous detail, and much more. Examples of these programs are Adobe Photoshop, Adobe
Illustrator and CorelDraw.

4. Database management systems:

Database management software is a collection of computer programs that allow storage,
modification, and extraction of information from a database in an efficient manner. It supports
the structuring of the database in a standard format and provides tools for data input, verification,
storage, retrieval, query, and manipulation. When such software is used, information systems
can be changed much more easily as the organization’s information requirements change. New
categories of data can be added to the database without disrupting the existing system. It also
controls the security and integrity of the database from unauthorized access. FoxPro and Oracle
are database management systems.

5. Presentation applications:

A presentation is a means of assessment, which requires presentation providers to present
their work orally in the presence of an audience. It combines both visual and verbal elements.
Presentation software allows the user to create presentations by producing slides or handouts for
presentation of projects. Essentially, such computer programs allow users to create a variety of
visually appealing electronic slides for presentation. Microsoft PowerPoint is one of the most
famous presentation application.

6. Desktop publishing software:

The term desktop publishing is usually used to describe the creations of printed
documents using a desktop computer. It is a technique of using a personal computer to design
images and pages, and assemble type and graphics, then using a laser printer or image-setter to
output the assembled pages onto paper, film, or printing plate. These softwares are used for
creating magazines, books, newsletters, and so on. Such software assist in creating sophisticated
documents including complicated page designs, detailed illustrations, and camera-ready types
faces. Quark Express and Adobe PageMaker are desktop publishing software.

STORAGE UNIT

 The purpose of the storage unit of the computer is to store the data entered before
processing and also to store the results after processing. The Central Processing Unit [CPU] is
the brain of any computer system. In a computer system all major calculations and comparisons
are made inside the CPU. The CPU is also responsible for activating and controlling the
operations of other units of a computer system.

There are two types of storage devices.
a. Primary storage device
b. Secondary Storage device.

a. PRIMARY STORAGE DEVICE OR RANDOM ACCESS MEMORY [RAM]:

Primary storage is usually referred to as Random Access Memory [RAM] because it is possible to randomly select and use any location of this memory to directly store and retrieve data and
instructions. It is also referred to as read/write memory because information can be ‘read’ from a RAM chip also be ‘written’ into it.

The Random Access Memory requires some times for accessing data and is considered to be the fastest memory. Each bit in a RAM stores information by means of electric charge, where the presence of an electric charge indicates ‘1’ and the absence of an ‘0’. RAM is called Temporary storage, because data persists until the machine is on.

ROM

A Read Only Memory [ROM] is one in which information is permanently stored. The
information from the memory can only be read and it is not possible to write fresh information
into it. This is the reason why it is called ROM. When the power supply is switched off, the
information stored inside ROM is not lost as it is in the case of a RAM chip. ROMs are mainly
used by computer manufacturers for storing the micro programs so that they cannot be modified
by the users.

b. SECONDARY STORAGE DEVICES

This section of the memory is also referred to as backup storage because it is used to
store large volume of data on a permanent basis which can be partially transferred to the primary
storage as and when required for processing.
The storage capacity of the primary storage of today’s computers is not sufficient to store
the large volume of time handled by most data processing centres. As a result, additional
memory, called auxiliary memory or secondary storage, is used with most computer systems.
Hard Disk, Floppy Disk, Tape and Compact Disc are the main secondary storage devices.

i). Hard Disk:

The hard disk used in the PC is permanently fixed, hard disks with storage capacities of 8 GB, 10GB,
20GB, 40GB, are quite common, the CPU can use the hard disk to load programs and data as well as to store data We should operate the PC within a dust-free and cool room (Preferably air-conditioned) to prevent hard disk crash.

ii). Floppy Disk:

Floppy disk is flexible circular disk of diameter 3.inches made of plastic coated with a magnetic material. This is housed in a square plastic jacket. The floppy disk can store 1.4 Mbytes of data [also called 1.44Mnytes, since it holds 1440Kytes]. Data recorded on a floppy disk is read and stored in a computer’s memory by a device called a floppy disk drive[FDD]. A floppy disk is inserted in a slot of the FDD. Some of the floppies have limited life time. The floppies have to be recycled periodically
to keep them alive. A frequently recycled floppy. [i.e used] will have a life time of 3to 4 years to do recycling take out old floppies occasionally and try to read them once, at least the directory.

iii). Compact Disk:

CD-ROM [Compact Read Only Memory] uses a laser beam to record and read data along spiral tracks on a 51/4’’ disk. A disk can store around 650/00MB of information. CD-ROMs are normally used to store data as back up. Using a CD Writer, lot of information can be written on
CD-ROM and stored for future reference.

iv). Tape Drives:

Even though tape drives are one of the oldest of storage technologies, they can still hold
the most data on a single cartridge. A computer tape drive works similar to a tape recorder or a
VCR. A plastic tape ribbon is coated with magnetic particles which are polarized by a magnetic
field generated by the read/write head.
Since tape is a sequential, and not a random- access media, a tape drive has to wind
through a tape to locate a specific bit of data. This makes accessing data slow so tape is mainly
used for system backups and regular archiving of files and records.
Tape dives allow users to backup large amounts of data. Tape drives are capable of
backing up a couple hundred megabytes to several gigabytes of information without having to
spend large sums of money on disks.

 iv). DLT [Digital Linear Tape]

DLT drives are a robust and durable medium. The DLT segments the tape into parallel
horizontal tracks and records data by streaming the tape across a single stationary head. Released
in 1991 DLT drives are very reliable, high-speed, and high-capacity making the DLT drives an
excellent use for Network backups.

DAT [ Digital Audio Tape ]

The popular choice for tape drives is DAT. This format is best known for digital audio recording
although DAT drives can’t play DAT audio. These drives use a recording technique called helical
scanning which is used in VCRs. The 4mm tape is wrapped round a spinning read/write head that records data in overlapping diagonal tracks. These overlapping tracks allow for high data density and faster data transfer speeds. There are a few DAT standards but the most common is Digital Data Storage [DDS]. DAT tapes can hold 2GB [SSS] to 40GB [DDS-4] of compressed data.

 v). Micro Vault USB Storage Media

Micro Vault media plugs directly into the computer’s SB port – and acts just like another drive. It is small, light, Shock-proof and moisture – proof. This nifty flash memory storage device is compact and durable enough to carry in any pocket. The device is recognized automatically when we connect it to the computer. By connecting it via USB, the files can be transferred by dragging and dropping. There are no cables or adaptors needed, no power cord and no driver software to install. It’s compatible with both Macintosh and Windows operating systems, and even comes with software that password protects the contents of the device.
They are perfect for sharing PowerPoint presentations, digital photos, MPEG video and
MP3s, transporting files between work and home, or sharing files with friends and colleagues.

CENTRAL PROCESSING UNIT [CPU]

The Central Processing Unit [CPU] is the brain of any computer system. In a computer system all major calculations and comparisons are made inside the CPU. The CPU is also responsible for activating and  controlling the operations of other units of a computer system. The control unit and the arithmetic logic unit of a computer system are jointly known as the Central Processing Unit. While the control unit takes care of the flow of data from input unit to storage unit and the flow
of final results to the output unit, the arithmetic logic unit is the place where the actual execution of instructions taking place during the processing operation.

The Central processing Unit consists of the following main components:
Switched Mode Power Supply [SMPS] - for converting the current voltage, Mother Board [ROM]. Arithmetic Logic Unit [ALU], Control Unit[Ram],Hard Disk – Storage unit, Floppy Disk – storage Unit, CD ROM – Storage Unit

INPUT UNIT

The input unit is used for entering the data and instruction into the computer for
performing computation of the data. The input unit accepts or reads the list of instructions and
data and converts these instructions and data in computer acceptable form. It supplies the
converted instructions and data to the computer for further processing. The devices used for this
purpose are called as Input Devices. Key Board and Mouse are the important input devices used
in our offices. Light pen, Joy stick, tracker ball, Touch pad, Scanner and Pointing stick are some
of the Input Devices.

a) Key Board:

The keys in Computer keyboards are almost similar to the keys in a typewriter but in addition
there are some special operational keys carrying special symbols that help us in giving
instructions to computer.

b) Mouse:

Mouse is an essential component in the modern computers which use Windows and other Graphical Use Interface [GUI] applications. Mouse is a small service in which a small ball is kept  inside and the ball touches the pad through a hole at the bottom of the mouse. When the mouse is held in hand pushed along a flat surface [mouse pad], the ball inside the mouse rolls and this movement of the ball is converted into electronic signals and sent to the computer, now we get advanced versions of mouse like optical mouse, scroll mouse cordless mouse etc. using the mouse the cursor [the small blinking vertical line we see in the monitor ] can be moved in any direction. The mouse is used for selecting
part or full text or object, and also for dragging and dropping the selected text or object.

How to handle the mouse?

When we slide the mouse left across the mouse pad the mouse pointer of the screen
moves left on the screen. When we slide it right the pointer moves right. When the mouse is
moved forward or backward, it causes the pointer to move up and down.
The following actions are performed with the mouse:
Clicking:
Keeping the mouse pointer at any position, if we click the mouse button the cursor will
move to that position.
Selecting:
To select a text for copying or deleting, keeping the mouse pointer at the beginning of the
text, click the mouse button [left button] and without releasing the finger move the mouse till the
end of the text and then release the finger. The text thus selected is highlighted and can be copied
or deleted.

Dragging:
After selecting the text as above, bring the mouse pointer at the selected text, press the
left mouse button with the finger and without releasing the finger drag the selected text to any
desired position.
Right clicking:
By pressing and releasing the right mouse button, the short cut menu is activated.

c) Scanner:

Scanner is an image acquisition device connected to the computer, which captures either
an image of a text document or a picture and transfers it into bits of information, which a
computer can understand and manipulate.

How does a scanner work?

The scanner uses a light source, typically a cold cathode lamp to illuminate the scanned
object. The light is then reflected off the object and into Charged Coupled Device [CCD]. The
Charged Coupled Device collects the information, and through a series of electronic devices
converts the analog signal into as series of digital signals which can then be read and processed
by a computer.

Uses of scanners:

Optical Character Recognition OCR – We can convert text based document images into
text that can be edited by a word – processing software. Enrich our presentations and documents
by adding images. Convert hard-copy images or documents into a fax format for faxing or for
record purpose. Add scanned images to our e-mil to enrich the content.
Type of scanners: Flatbed Scanner, Sheet fed, Handheld, Card scan.

• Flatbed Scanner: The flat bed scanner as shown in the illustration is one of the most commonly used and most recommended scanners. This scanner allows the user to place a full piece of paper, book, magazine, photo or any other object onto the bed of the scanner and have the capability to scan that object.A sheet containing text can be scanned using the scanner and saved as an image file. There is

software to convert the image file once again into a text file.

• Sheet fed scanner:  This scanner allows us to scan pieces of paper. The sheet fed scanner is a less expensive solution when compared to the flatbed scanner.
• Handheld Scanner: The handheld scanner allows the user to drag over select sections of pages, books, magazines, and other objects scanning only sections. However it can be tedious to drag the handheld correctly which can cause distortion in the image being scanned.
• Card scan Scanner: This scanner is mainly used to scan visiting cards for creating data base of the addresses.

 d) Punched cards

Punched cards are still in use as medium for recording data and instructions in the form
of punched holes to denote and then they are sequentially read by the card Reader. The card
Reader sends the data and instructions to the CPU to process them. The punched cards used for
data processing are made generally of 80 columns and 12 rows. Today 96 columns cards are
available. In these cards a hole in punched to represent the binary l. The absence of a hole
represents binary 0. If a card is punched wrongly, it cannot be corrected. Further, the punched
cards are not reusable, i.e., cannot be used for any other data. Many numbers of cards are
required for the computer programs. Such a collection of cards is called a deck. Each card has
the left top corner cut to identify the arrangement of the cards is correct or not. The cards are
read by a Unit called a card Reader. The punched cards are placed in the Read Hopper after
verification. On receiving the command from the control unit the device moves the cards one by
one over two sub-devices. One of which, sense the punched holes (0s and 1s) and transcribes the
pulses to the CPU. Then the output is given as per user specification.
Advantages
1. It is very easy to read data on the cards
2. The cards are less expensive than other storage media.
3. It is much simple to operate.
4. After inserting a card, if an error is detected, the whole system stops functioning.
Disadvantages
1. Punched cards are bulky when put together, so they require large space to store them.
2. The cards are easily damaged and perishable.
3. Transfer of data is relatively very slow.
4. An incorrectly punched card cannot be corrected, it must be replaced.
5. Unit Record machines require manual intervention at every stage.
6. Data is not processed in ordinary language. It has to be translated into something we can
understand.

 e) Paper Tapes

The punched paper tape is a continuous strip of a paper about one inch wide and up to
300 meters long. The characters are recorded on tape, which may be 5 or 8 as per the design of
the tape. These punched positions are called as channels. It is the oldest media, of input and
output media. Her also, a hole represent 1 and its absence represents 0. Data from the tape is read
through a Tape Recorder per second. The tape comes in various forms viz., Oil paper, dry paper,
metalized paper and laminated paper.
Advantages
1. Compared to the punched card, it is more compact and economic on storage.
2. It is less in weight and easy for mailing etc.
Disadvantages
1. Since the roll is so long, correcting or inserting data can be very tedious process and time
consuming.
2. The life of the paper tape is short. This makes it inconvenient for storing over a long period.
It is not durable.
3. Moreover, it is sequential data processing medium.

f) Magnetic Tape

Because of the problems faced in the paper media, magnetic substances have come. First
among these was the magnetic tape. This is also a sequential media for normally between 1.25-
2cms. Wide and up to 900 meters long. It is made of plastic with a metallic magnetic oxide
coating on one side. Generally, data is recorded on either a 7 parallel-rack-tape or on a 9 paralleltrack-
tape. Writing on and reading from the tape is done with the assistance of READ/WRITE
head. The number of characters per inch length of tape stored is called the 'density' of the tape.
This varies from 550 to 1600 or even 16K. The 9 Track tapes have the higher densities. Then
comparing with the punched card and punched tape, the magnetic tape has certain advantages
and disadvantages.
Advantages
1. Data are stored very compactly.
2. It is very easy to handle the Magnetic Tape than the Deck of Cards.
3. The Magnetic tape costs less than the cards.
4. It requires less storage space for data and therefore has a large capacity.
5. It is reusable i.e., the old data can be wiped out and fresh information could be recorded on it.
6. The speed of transferring the data is very high comparing to paper devices.
Disadvantages
1. In magnetic tapes, the data has to be accessed sequentially. This makes the retrieval of data
slow.
2. The punched cards can be read visually, whereas to read the magnetic tape a I machine is
needed.
3. The tape is subject to the usual wear and tear of time.
4. Data will be erased if the tape is exposed or placed nearby any Magnetic field or high voltage
circuits.

g. Magnetic Disk

It is yet another step in the evolution of Input/Output devices. The Magnetic Disk has an
advantage over the punched cards and Magnetic Tapes i.e., the data stored on a disk can be read
randomly while in the magnetic tape, the data are read sequentially. Random access is that the
particular record in the file can be detected directly and the access time is saved. In Magnetic
disk the record is accessed in a fraction of second i.e., less than 0.01 sec. The disk varying in
diameter are generally coated on both sides with magnetic oxide. Each surface of the disk is
divided into a number of sectors, called storage segments. The storage segment is a specific
portion of a specific side of the disk. A segment can store one or more record of a file, which will
vary according to the size of the record. While searching, a particular record can randomly be
selected and directly accessed, because, each storage segment is uniquely marked by an address
with side number, track number, sector number etc.

h. Joysticks and Trackballs

Joysticks provide an alternative method for feeding the computer visually interesting
data. When you move the joystick, cursor on the screen moves in a corresponding way. A
trackball is a plastic sphere mounted in a socket so that it is free to rotate in any direction.
i. Touch Screens
Touch Screens are another favorite "user friendly" method for feeding data into
computer. User can command the computer to perform various useful tasks simply by touching
specific sectors of the screen with their forefingers. The computer senses the Location of the
finger in various ways.

OUTPUT UNIT

The results of the data processed by the computer are available in electronic signals. The
output unit converts these signals into a form which could be easily understood by us. The
output is usually given either on the screen by visual display unit/monitor or in a printed form by
printers.

a) Monitor (Visual Display Unit or Screen)

The monitor is made up of cathode-ray tube CRT due to which it also called C.R.T terminal. The screen consists of horizontal and vertical sweep circuits similar to T.V. sets. The screen’s inside is
coated with dots of phosphor called pixel and can be used for games or graphics or displaying the
results of a calculation done by computer. The more the number of pixel or dots in a screen, the better will be the capability of computer to display an information.
This capability is known as resolution. The characters typed with the keyboard are displayed on the screen. We can thus verify whether the programs we enter into computer is corrector not.

Tips for avoiding computer vision syndrome:

Long hours of staring at a computer screen causes dryness and reduces the blinking rate
of the eyes. Burning, itchiness and watering of eyes are the common visible syndromes of
computer vision syndrome. Often headache is a direct consequence of the glare emitted by the
screen.

•  To avoid the syndrome the following measures are to be taken:
•  Make sure that the computer screen is not too close to your face.
•  Position the screen so that it is either at eye level, or slightly lower.
•  Tilt the monitor slightly to eliminate reflection or glare.
•  Make sure that primary light source [such as windows] is not shining into your face or directly on the monitor.
•  Frequently look away from the screen and focus on far away objects.
•  Reduce the contrast and brightness of the screen by adjusting the controls on the monitor.

 b) Printer

Printer is the most commonly used output device. It is used to prepare permanent
documents in human – readable form [hard copy]. The are several types of printers that are
designed for different types of applications.
Printers are of two types-impact and non impact. Impact printers use the familiar
typewriter approach of hammering a typeface against paper and inked ribbon. Non- impact
printers do not hit or impact a ribbon to print. They use thermal, electrostatic, chemical and
inkjet technologies.
Depending on their speed and approach of printing, printers are also classified as
character printers, and page printers.

Types of Printers:

1. Dot Matrix Printer:

In this printer characters to print are made up of a finite number of dots and so, the print head consists of an array of pins. Characters to be printed are made up of a finite number of dots and so, the printer. The character code is decoded by the printer electronics and activates the appropriate pins in the print head. Many dot matrix printers are bi-directional. i.e., they print from left to right as well as from right to left on return. This enhances the speed of printing. The printing speed is around 300 characters per second.

 2. Line Printer:

Unlike a dot matrix printer, line printer prints a complete line at a time. Two types of line printers are
available.

3. Drum Printer

It consists of cylindrical drum. The characters to be printed are embossed on its surface.

4. Chain Printer:

It has a steel band on which the character sets are embossed. Printing speed varies from 150 lines to
2500 lines per minute with 96 to 160 characters on a 15 inch line. Six to eight lines per vertical inch are printed. Usually 64 and 96 character sets are used with English letters.

 5. Inkjet Printer:

It consists of print heard, which has a number of small holes of nozzles. Individual holes are heated very rapidly by an integrated circuit resistor. When the resistor heats up, the ink near it vaporizes and  is ejected through the nozzle and makes a dot on paper placed near the head. A high – resolution inkjet printer has around 50 nozzles within a height of 7mm and can print with a resolution of more than 300 dots per inch. Latest inkjet printers have multimedia heads, one per color , which allow color printing. The printing speed is around 120 characters per second.

6. Laser Printers:

• In laser printer an electronically controlled laser beam traces out the desired character to be printed on a photo conductive drum
• The drum attracts an ink toner on to the exposed areas.This image is transferred to the paper, which comes in contract with the drum. Very fast printers print 10,000 lines per minute. These printers give excellent outputs and can print a variety of fonts.
• Low speed laser printers, which can print 4 to 16 pages per minute, are now very popular.

NETWORKING AND ADVANTAGES OF NETWORKING

 With standardized hardware and software, the microcomputers provide user-friendly
environment. It meets the computing requirements of most users. But, the need for interaction
with other computer users and with other computer systems for exchange of data etc., has
increased over the years. Networks are increasingly meeting this need. From the users’ point of
view the networks may be of two types: Local area network and Wide area network.
Computer networking is the process of inter connecting two or more computers so that
the users can communicate with each other, share resources and overcome other limitations of
stand-alone systems. The network can be established with a variety of combinations of
computers such as a net of only microcomputers, microcomputers and one or more
minicomputers and a set of microcomputers connected to a mainframe computer. The computers
in typical network are autonomous in the sense that they have processing capability independent
of the network.

ADVANTAGES OF NETWORKING

The main advantages of networking are:
(i). Hardware resource sharing:
Network enables sharing of expensive resources such as processor, storage space and
peripherals like modern, fax, and laser printer.
(ii). Sharing of databases:
The network permits concurrent access to the same data file by many users in the
network. Thus, user in the sales department, production department, inventory department etc
share corporate databases.
(iii). Sharing of Software:
Any user in a network can load and use the software installed on any of the computer of
fileserver in the network.
(iv). Communication between users:
The Network users can communicate between them. E-mail facility can also be used for
communication.
(v). Decentralized data processing:
In a network, the data processing can be decentralized by enabling local offices to capture
and store data, and generate information to meet most of their requirements a local level itself.
(vi) Security of data:
In a networked environment the data is backed up with duplicate storage. Adequate
security measures are also put in place to product the data.

TYPES OF NETWORK

The networks can be classified into three; local area network (LAN), metropolitan area
network (MAN) and wide area network (WAN). They are explained in the following sections:

Wide Area Network (WAN)

WAN is made up of number of autonomous computers distributed over a wide
geographical area. WANs were originally developed in the late 1960s to enable communication
between computer centers and sharing of hardware, software and other communication facilities.
WAN can be implemented using private or public networks. In a private network an
organization takes on lease telephone lines to connect such sites into a network. It is also
possible to connect computers in different locations using microwave or satellite transmission.
Public networks are installed by the Government owned telecommunication agencies. WAN
spans large geographic distances. It is also called long-haul network. WAN is usually operated
at lower speeds then MAN and involves delay.
Most organizations use private networks for communication. Society for Worldwide
Inter bank Financial Transactions (SWIFT), a non-profit organization of banks, owns a private

 network. The network exchanges financial transactions between the participating financial
institutions, about 3000 in number in over 60 countries. The terminals of these participating
banks are hooked with SWIFT’s access centers. The network offers data communication service
24 hours a day, 7 days a week.
INDONET, NICNET, SBINET and WELCOMENET are some of the private network in
India. CMC’s INDONET offers e-mail service to customers for a fee. NICNET is a network of
National Informatics Center that connects all the district headquarters in the country. SBINET is
a private network of State Bank of India and connects its branches across the country.
WELCOMNET connects the hotels of the Welcome Group.

Features of Wide Area Network

A wide area network (WAN) is used to connect LANs and nodes that are separated by
great physical distance. Generally speaking it is larger version of LAN with several differences:
1. It operates by means of the international telephone network
2. Unlike LANs which owned by their users, WANs operate on public and leased
telephone lines provided by licensed common carriers, or by other means such satellite
and microwave, which are regulated by government agencies.
3. Data transmission is somewhere slower.
4. The WAN compose any of the following system configurations:
5. Single nodes
6. Clusters
7. LANs
Suppose a company has its central headquarters in Coimbatore and the Coimbatore site
contains all departments and equipment for product manufacturing prod distribution, accounting,
and sales. The information pertaining to these operations is tracked by a single centralized
database system. As the company becomes more profitable and expands, it established additional
sales offices on Mumbai and Delhi. Each sales office maintains its own system to record and
track customer orders for its region. At the same time the two sites are linked to the mode at
corporate headquarters and relay each order shipment and inventory and invoice processing.

Advantages of WAN

The integration of the local nodes into the distributed database linked by the WAN
provides the following advantages:
1. The WAN allows access to database at remote sites, enabling exchange of data.
2. If a remote node fails, remaining nodes on the network can still exchange data.
3. If the network fails, the local mode can still access its own database.
4. The data used on daily basis by the sales offices resides at the local site, making it easier to
retrieve quickly.
5. The local offices can maintain the data more effectively. The corporate office can access the
data as needed.
6. As a site's database grows larger, its system's storage capacity can be easily upgraded without
affecting the transfer of data between other nodes on network.

One of the most significant aspects of a wide area network when comparing it with
freedom of a local area network is the involvement of a public telecommunications authority.
Regardless of whether the network is made up from system, the controlling authority is almost
always the public authority. In order to protect their equipment and employees, the authority lays
down rules, which must be observed by anyone connecting to their lines. In most countries
stringent requirements are also imposed on the characteristics of the data transmissions.

Metropolitan Area Network (MAN)

Metropolitan area network covers a wider area than a local area network. Usually MAN
covers a large metropolitan city and is a scaled down version of wide area network. It operates
at high speeds over distances sufficient for a metropolitan area.

Local Area Network (LAN)

A LAN is a system of interconnected microcomputers, sharing common resources like
disks, printers etc., and links a number of computers workstations) together to allow many
people to use the same software and data files. Each user in such a multi-user environment
accesses the resources through his microcomputer workstation. The network operating system
integrates all the network components and makes operation smooth and transparent. LAN works
in restricted geographical area such as within a large building or offices within a few kilometers.
The LAN is an interconnection of computers that need to communicate with each other in a
limited geographical area. The network may have other sharable devices attached such as fax,
laser printers and copiers. The network includes a central facility with huge storage capacity for
the requirements of the organization. It also has a network operating system for managing the
network.

Types of LAN:

Local area networks are mainly of two types: Client/ Server LAN and Peer-to-Peer LAN.
a) Client / Server LAN
Client Server LAN has servers and clients. The server is a computer that manages shared
resources: hardware as well as software and data. It is usually a powerful computer with large
RAM and secondary storage capacity. The LAN has a number of microcomputers, called
clients, the request the server for services. The LAN may have many servers each specializing in
one area of service such as file server, printer server, database server etc. A file server stores
program and data files. A database server stores data and a printer server controls printers on the
local area network.
b) Peer-to-Peer LAN:
In a Peer-to-Peer LAN every computer is equal in status and functioning. All the
computers on the network are capable of communicating independently with any other computer
on the network without using a server. Thus, any computer on the network can access data and
programs stored on any other computer. The peer-to-peer LAN is less expensive than
client/server LAN. But at the same time this LAN may be slower than a client/server LAN.

LAN Topology

The design of network requires selection of a particular topology and an architecture for
the interconnection of network component.
Topology refers to the way the computers are physically connected into the network. The
network architecture includes the specifications of the components that can be connected to the
network. IBM’s Systems Network Architecture (SNA) is an example of vendor developed
network architecture. Such network architecture specifies network components such as
terminals, workstations, printers, cluster controllers, host computer and communications
controllers.
There area a number of network topologies. Of them ring, star and bus are popular network
topologies.

a) Star Topology:

In star network the nodes are connected to a central computer called the host computer.
The nodes cannot communicate directly. Each node can communicate with the host computer.
The host computer takes the message and routes it to the other node or nodes.

 In a star network centralization of control over the network resources is easy. It is also
possible to network minicomputer or mainframe with other microcomputers and dumb terminals.
It eliminates single point failure of a common wire. If one of the host computers fails, it does not
usually affect the others in the network. But the hub becomes a central point of failure in a ring
network. If the host computer breaks down, the entire network breaks down.

b) Ring Topology:

In a ring network the computers can communicate directly with each other and also with
the central computer. The nodes are connected to a line that is closed like a loop. The ring
network is more reliable than star network. Even if the central computer in the network fails, the
other computers can continue to communicate with each other.

 c) Bus Topology:

A bus network configures computers to a single non-looping channel. The computers
connected to the network share the same bus or communication channel. Bus wiring is easy and
needs much less wring for small segments.

Old Ethernet bus wiring is prone to cable failure. If the bus wiring connection is broken
at any point, the entire network fails.

d) Hybrid Network:

In most cases, instead of a single topology, a combination of topologies may be used for
greater flexibility and reliability. Hybrid network combines features of Star, Ring and Bus
network:

Features of LAN

The features of LAN include the following
a) Limited geographical area say within a few kilometers.
b) Common communication link for sharing information, software and peripheral devices
without regard to proximity of user to such resources on the network.
c) High transmission capability.
d) Low error rate as the network contains built-in component for detecting for system errors.
e) Private ownership by the user.
f) Not subject to regulation by the telecom service.

LAN interconnects computers and computers and components within a limited
geographical area. Such LANs are normally set up within a single site can have one or more
business complex, a hospital, an office- building etc. The site can have one or more buildings but
they should not be too for a way, say less then5 kilometers. A LAN can also include a variety of
computer systems and devices such as workstations, microcomputer, file servers, plotters,
scanners, graphic terminals and printers.
A large personal computer or mini computer serves as the LAN’s hub. A high capacity
hand disk is attached to the hub as data files and software are stored on the network file server.
The users can load the software on the file server and retrieve data files for processing. The
output can be directed to the printer attached to the LAN.
Any the communication network that meets most or all of the following characteristics
can be classified as LAN:
a) All the devices on the network share a common transmission medium, that is, the cable and/
or the controller.
b) The devices connected to the network can operate independent of the network.
c) Any device connected to it can communicate with any other device on the network, and
d) The network is capable of supporting heavy data traffic over short distances compared to
telecommunication network.
e) The network covers a limited area usually a few kilometers in radius or a single site like a
university campus, an office or a factory.

LAN Components

The components of LAN are File server, workstation, network operating system, LAN
cable, Active and Passive hubs etc.

a) Workstation

It is a single-user microcomputer with high power communication facilities. It can
exchange message with other workstations or fileserver.

 Workstations can be of two types: user workstation and server workstation. User
workstation is a microcomputer on the network, which is used to access the network. Service
workstation performs service to process other workstations on the network. User workstation
normally does not process requests from other workstations. Server workstation makes available
all sharable network resources to other workstations. More than one server workstations may be
added to the network such as printer server and fileserver. Normally the server workstation is
the most powerful workstation. Server workstation may be dedicated or non-dedicated. In case
of dedicated workstation, it is not available for other user applications. Non-dedicated server
workstation doubles as an individual workstation and at the same time performs network-related
functions.

b) File Server

File server is actually a process running on a computer that provides the clients access to
files on that computer. The term is loosely applied to mean computer that runs file server
software. In this sense, it is a powerful computer with special software to serve files to other
workstations on the network. The files, which may be program files or data files, are
simultaneously shared by a number of workstations. Novell Netware is a popular network
operating system.

c) Gateway

The gateway assists in communicating between LANs. A workstation may be dedicated
to serve as gateway. This is required particularly when two networks with different technologies
have to communicate with each other. Gateway may also be used to connect LAN with a
mainframe computer.

d) Network Interface Unit

The network interface is a printed circuit board installed in the microcomputer. It may be
called network card, network adapter or network interface unit. It connects the workstations
functionally and physically with the network.

e) Active Hub

Hub is an electronic device to which multiple computers are attached usually using
twisted pair cables. Active hub is a powered distribution point with active devices that drive
distant nodes up to one kilometer away. It can connect up to eight nodes on the network. The
maximum distance carried by an active hub is about 2000 ft.

f) Passive Hub

This hub is a distribution point that does not use power or active devices in a network to
connect up to four nodes within a short distance. The maximum distance covered by a passive
hub is nearly 300 ft.

g) LAN Cable

LAN requires superior cable capable of transferring data at high speed. Coaxial cables or
fibre optic cables may be used for networking computer.

h) Network Operating System (NOS)

The NOS integrates all the network components. The NOS facilitates file and print
serving along with other functions like communications and e-mail between workstations. In
most LANs the NOS exists along with the computer’s operating system.. The computer’s
operating system processes the system requests first and processes them if they can be done with
the workstation resources. If it is not a local request, meaning that the network resources have to
be used, the request is transferred to NOS for carrying out. Thus, the NOS is responsible for
controlling access to data, storage space and sharing of other peripheral resources.

i) Applications Software

Another component of LAN is application software. It has to be ensured that the
application software works in the multi-user environment.

j) Protocols

Data transmission between devices requires protocol. Protocols are sets of rules and
procedures to control the data transmission between computer and other devices. They are
common technical guidelines for communication between devices. They specify the order in
which signals will be transferred, the signal for completion of transfer etc. Only Devices using
the same protocol can communicate directly. Both the sending and receiving devices must use
the same protocol for effecting communication. For communication between devices using
different protocols requires intermediate interpretation device or software.

The protocol performs the following functions:

a) Set up a link with the other device in the communication.
b) Identify the component to other components in the communication (sending device’s
channel ID)
c) Send and interpret the data
d) Provide a continuous feedback on data transmission like data is not being received and
understood.
e) Request for retransmission of garbled data.
f) Engage recovery procedure when error occurs.
g) Provide an acceptable way of terminating transmission so that all devices have completed the
process.
The protocol is embedded in communication software designed to use a particular protocol.
The user need not bother about the protocol as the components involved in the communication
perform the protocol matching. The data communication protocols are of two main types:
asynchronous and synchronous. The synchronous protocol permits continuous data
transmission. The devices in communication must be synchronized with the other. The
transmission is governed by a time interval and not by start-stop bits. For example, clock, in the
modern, sets the time interval.

DATA PROCESSING SYSTEMS

 The methods of data processing depend upon the following factors:
(a) Volume of data to be processed
(b) Complexity of data processing operations
(c) Computational demands
(d) Processing time constraints and
(e) Economic factors.
Various methods or modes of data processing are given below:
(i). The single user system
(ii). Batch processing
(iii). Multi-programming
(iv). On-line Processing
(v). Real-Time processing
(vi). Time sharing concept
(vii). Distributed processing

The methods of data processing are explained below:

The single user system

It is one-man show and is indicative of one of the earlier stages of computer
development. Here only one person can work at a time. Hence, especially if the machine is
meant for the use of many persons, much computer time is wasted waiting for one person to
finish and debug his program on the machine.

Batch Processing

This is an old system but even today it is used for data processing in computing
machines, in which the capacity of the CPU is limited. In this system, the data is collected for a
predetermined period of time, after which it is accumulated in sequential manner.
In this system the source transaction documents are first collected before being sent to
computer room. A batch of transactions is entered onto a computer media by data entry devices.
The transactions are validated during data entry and verified with the source documents from the
check lists. The validated and verified results on reports are returned to the user departments. In
batch processing system the emphases is on maximizing the computer resource utilization.
In batch processing, the processing cycle called Batch processing cycle repeats itself at
every regular intervals. The elements this cycle are given below:
(i) Data capture.
(ii) Data transmission.
(iii) Data transcription, verification and validation.
(iv) Job Processing.
(v) Job assembly putting together the batch for processing.
(vi) Job disassembly (separating out the reports after processing)
(vii) Reports and distribution.

Features

(a) Here, the data is accumulated into batches and processed periodically.
(b) The jobs are processed one after the other without any user interaction.
The concept of Batch Processing is dearly explained with the help of the following
diagram:

Examples of applications which can use batch processing are:
(1) Payroll Processing: In payroll processing the data are collected for a stipulated period of
time usually one month and processed at regular intervals after which payments are
distributed to all the employees.
(2) Telephone Billing: Here the subscriber does not get a bill for every call he makes. Instead,
his calls are recorded at a centralized place and are processed on a predetermined period of
time to prepare his bills.
(3) Financial accessing
(4) Budgeting and Budgeting control
(5) Production planning and control
(6) Project planning and control
(7) Project planning and control
Drawbacks in Batch Processing:
The following are the drawbacks of batch processing:
1. Time gap between capture of data
2. Time consuming to debug
3. Delay in generating reports

Multi-programming:

In batch processing, programs are executed one by one. The memory and ALU of the
machine are not being fully utilized. To get the maximum use of the machine, multiprogramming
system is used. “Multi-programming enables to store and execute more than one
program in the CPU at the same time”. The multi-programming concept is event based. The
purpose of multi-programming is to increase utilization of the computer system as whole.
Multi-programming is defined as execution of two or more program that all reside in
primary storage. Since the CPU can execute only one instruction at a time, cannot
simultaneously execute instructions from two or more program. However, it can execute
instructions from one program then from second program then from first again, and so on. This
type of processing is referred to as concurrent execution. Using concept of concurrent execution,
multi-programming operate in the following way:
When processing is interrupted on our program, perhaps to attend an input or output
transfer, the processor switches to another program. This enables all, parts of the system, the
processor, input and output peripherals to be operated concurrently thereby utilizing the whole
system more fully. When operating on one program at a time the processor or peripherals would
be idle for a large proportion, if the total processing time, even though this would be reduced to
some extent by buffering. Buffering enables the processor to execute another instruction while
input or output is taking place rather than being idle while transfer was completed. Even then,
when one program is being executed at a time, basic input and output peripherals such as floppy
disk drive and line printers are slow compared with the electronic speed of the processor and this
causes an imbalance in the system as a whole. However, in a multi-programming environment
the CPU can execute one program's instructions while a second program is waiting for I/O
operations to take place.
In a system of multi-programming storage is allocated for each program. The areas of
primary storage allocated for individual programs are called ‘partitions’. Each partitions must
have some form of storage protection and priority protection to ensure that a program must have
some form of storage protection to ensure that a program is one portion will not accidentally
write over and destroy the instructions of another partition and priority (when two or more
programs are residing in primary storage) because both programs will need access to the CPU's
facilities (e.g.; the arithmetic and logic section) A system of priority a method that will determine
which program will have first call on the computer's facilities is normally determined by locating
the program in specific partitions.
Programs that have the highest priority normally are stored in an area called the
‘foreground partition’. Programmes with lowest priority are stored in an area called ‘background
partition’.

On-Line Processing

Definition of Online Processing:

Online processing refers to processing of individual transactions as they occur from their
point of origin as opposed to accumulating them into batches. This is made possible by such
direct access devices as Magnetic disk and Magnetic Drum and number of terminals connected
to, and controlled by a central processor. In this way, various departments in a company can be
connected to the process by cables. If operating companies are a number of miles away from the
processor then they are linked by means of telegraph or telephone lines. This type of processing
provides multi access to information files by terminal users and also enables them to update with
transactions data.
It is a non-sequential process in which data is directly transmitted between input/ output
device and a computer system via communication links. It is a method of processing where many
users have direct access to the same system, and where the file is updated as soon as the
transaction is completed.

Special Features

1. In this method data is not accumulated, instead it is entered and executed directly.
2. Quick Processing - By means of direct communication with the computer and continuous
flow of input, the delay between transactions and their processing is avoided.
3. This method reduces the data entry errors, because the user who generates, the data is the one
who keys it in.
4. This system validates data at various points and ensures that correct data is being entered.
5. Under this method the system performs the whole task in a conversational 'manner helping
the data entry process.
6. In on line processing, one has the latest update immediately.

Online processing ensures that the records are in updated at any time whereas this is so
with batch processing say once a week but the fact remains that online processing is usually
more costly. Therefore in choosing one of the processing both updating of records and costs are
to be considered.

 On-line Applications:

Systems are being developed and are already in use for a wide range of application in
different type of industries described below:
a. Electricity and Gas Boards: By means of terminals situated in showroom it is possible to
inform perspective customers of the availability of the appliances in response to their
inquiries.
b. Banking: It is possible to inform bank customers of the status of their accounts in
response to an inquiry by accessing relevant file using on online terminal.
c. Tour Operators Reservation Offices accept telephone inquiries from travel agents
regarding the availability of holidays in respect of client's inquiries. By means of
terminals, the availability of the required holidays can be checked and booked
immediately.
d. Stock Exchange: Terminals located in major stock Exchange through out the country and
the offices of participating brokerage from enable the speedy processing of share
dealings.
e. Stock Control: Terminals located in warehouse provide the means for automatic
recording of stocks, updating of stock records, reservations, follow-up of outstanding
orders and the printing of picking list etc.,
Benefits provided by Online Systems: Online systems provide a number of benefits all of
which assist in improving administrative efficiency which is essential in today's competitive
business environment. A number of benefits are out-lined below:

a. Integration of clerical work with the computer:

On-line systems assist in harnessing activities of clerical staff to the computer by the use
of terminals. They can have access to information which they require for the efficient
performance of their jobs in dealing with customer enquiries and order processing.

b. Elimination of tedious tasks:

Routine clerical tasks are replaced by terminal operations providing a greater degree of
job interest, operating efficiency and job satisfaction.

c. Reduction in paper work:

Volume of paper work generated by normal clerical system and batch processing system
is relatively high. Online systems reduce the volume of print out required for management report
since the information can be displayed on terminal screen on demand.

d. Improved accuracy:

As terminal messages are checked accuracy before being transmitted to the computer by
data validation programs, the quality of formation in a system increases as the input errors are
reduced. Hence, information is more reliable.

e. File updating improved:

Master files are more easily updated by terminal key board with regard to transaction
data, as special runs do not require to be set up as is the case with batch processing applications.

f. Management Information more readily available:

Management information becomes more readily available by direct access facilities
which enables mangers to obtain a greater degree of control to the operations for which they are
responsible.

g. Improved customer services:

Improvements in the level of customers service can be expected in these systems
concerned with appliances sales, booking systems and accounting enquiries.

h. Reduced data preparations cost:

On-line system dispense with the need to convert human sensible data into machine
sensible data thereby eliminating punching and verifying operations. This saves time and the cost
associated with such operations.

Real Time Processing

It is also called as interactive mode or Direct mode. This system makes the user to have
direct contact with the computer through his terminal. It is an alternative approach to an on-line
processing system. Here the data is processed, the instant it occurs. There is no delay between
the time data is available, and the time it is processed.

The term real time refers to the technique of updating files transactions date immediately
after the event to which it relates occurs. This is in distinction to batch processing which
processes related data to batches of pre-defined periods of time. Real time systems are basically
on-line systems with one specially in inquiry processing. The response of the system to the
inquiry itself is used to control the activity. An on-line production data collection system that
simply accepts input and utilities it for payroll and costing purposes cannot be termed real-time,
but if, on the other hand, the system is designed to provide immediate information to monitor the
production processes, it is a real time system.

Special Features

(a) Program is always under execution.(b) It produces output to control, direct or affect the outcome of an ongoing activity or
process.
(c) In this method, the control is exercise during the actual functioning.
(d) It is meant exclusively to perform one task.
(e) It is like an online system with; title constraints on response time availability.
(f) It is called a real time system because it has to give results based on dead lines which
are imposed by the real world outside.
(g) The data which has to be produced by the systems has to be in such a less time, that they can
influence the external events which are based on this data.

Thus the response of a real time system is one type of feedback control system. The
response time would naturally differ from one activity to another. If the example, it is the
launching of a space vehicle, the response time should be in split second whereas in business
situation even a few minutes of response time may be alright. Online updating in real time
usually leads to transaction as a by-product. For example, the updating in real time a customer's
order may lead to such transactions as dispatch noted and purchase requests, etc. Real time
systems offer accountants and others in business a chance to fulfill the potential of the computer
as a tool of management.

Guided Missile System

Real Time Processing is suitable in the following type of business operations:
i. Wholesale supplier and manufacture - Availability of stocks.
j. Airline - Flight seat availability.
k. Manufacturing - Status of production orders.
l. Process Control.

Space Craft Control.

Real time systems usually operate in multi-programming and multi-processing: This
increases both availability and reliability of the system. CPU's in real time system should possess
the, capability of what is known as program interrupts. These are temporarily stoppage or halts in
the execution of a program so that more urgent messages can be handled on priority. It may be
worth noting that some computers systems are dedicated to real time operations and others are

designed to operate in both batch and real time modes so that they can also serve as stand by unit
to each other.

Time Sharing

It is a special type of on-line processing in which several users share the resources of an
on-line computer system to avoid turn about time, especially when results are needed quickly;
another system is available i.e., time sharing system. In this method the individual user has an
independent local terminal. The terminal is connected to a main computer, which does all the
processing work.
Under this system each person on a terminal has to log into the system. The system then
lists him in the order in which he has logged on. Once everybody has logged on, the system will
permit the first in the list to run his program. The time given for running the program is generally
10 milliseconds. It is called a time slice or a time slot or a quantum. Starting then, with the first
to log on, each user is given his time slice. Once all have made use of it, the system starts all over
again, repeating the cycle. The system maintained is called a polling system whereby each
terminal is polled on a round robin basis.
All the instructions given by the users are carried to the centrally located main computer
system and processed there and retrieve back by the user instantaneously. Since, the centrally
located main computer has high-speed processor, users may feel that they are sharing the same
computer resources.

Features

1. The processor time is shared between two or more persons.
2. The processor switches from one user's job to another at a rapid rate under the control
of a monitor program.
3. This concept is time based.

The concept of time-sharing can be explained with the help of the following diagram.

Let us suppose that there are three terminals, each person on a terminal has to log into the
system. The system then lists him the order in which he has logged on. Once everyone has
logged on, the system will permit the first on the list to run his program. The time given for
writing a program is called a time slice or time slot. Starting from the first, each user is given his
time slice. Once, all the three users have made use of it, the system starts all over again,
repeating the cycle. The sequence maintained is called Polling System. Most time sharing
systems respond to user's instructions in milli/micro seconds.

Advantages of Time-Sharing System

(1) Simultaneously several users can be served.
(2) All the users have the same priority.
(3) All the users get equal amount of processor time.
(4) The interaction with the running programs is possible.

Time-Sharing Vs Multi-programming

The difference between these two methods is that in "time, sharing" the CPU links only
one terminal at a time and its total time is shared uniformly by all the users. But in
multiprogramming, the CPU links more than one terminal or other peripherals at a time.
Therefore, multiprogramming more efficiently utilizes the main memory and the central
resources than time sharing. Time sharing is employed only for multi terminal system whereas
multi programming is meant both for single as well as the multi terminal system.

Distributed Processing

In computer science, a form of information processing in which work is performed by
separate computers that are linked through a communications network. Distributed processing is
usually categorized as either plain distributed processing or true distributed processing. Plain
distributed processing shares the workload among computers that can communicate with one
another. True distributed processing has separate computers perform different tasks in such a
way that their combined work can contribute to a larger goal, such as the transfer of funds from
one bank to another. This latter type of processing requires a highly structured environment that
allows hardware and software to communicate, share resources, and exchange information
freely. At the highest (and most visible) levels, such distributed processing can also require datatransfer
mechanisms that are relatively invisible to users but that enable different programs to use
and share one another's data.
Distributed data processing system is a network of several computers in remote stations,
each of which is linked to a single host computer. The larger, central computer maintains the
firm's master data base and system log. Each remote system is a fully independent computer that
maintains its own local data base in addition to communication with the master computer. These
individual computers are tied together through a high speed communication network. This allows
individual computers to communicate with one another in a variety of ways depending on the
CIS requirements.
Many small computers (called nodes) are employed as data collection points in several
departments. They are connected to a main computer system (called File Server) in a centralised
department, which controls the entire database. The processing involved here is known as
distributed processing.
The distributed data processing system exists because of the need for large interactive
installations with a high degree of reliability and accuracy. Moreover, large number of mini
computers can be connected in this system which results in cost reduction.

Features

(a) Decentralized computer system
(b) Interconnected by communication network (c) More reliable
(d) Since more than one computer is used in the network, it is economical.

Advantages:

Distributed data processing system has many advantages:
a. Local computers on the network offer immediate response to local needs.
b. Systems can be expanded in modular fashion as needed because many small
c. Computers are used as the system is not dependant on large unit that could shut down the
network if it failed.
d. Equipment operating and managing costs are often lower.
e. Minicomputers tend to be less complex than large systems; therefore, the system is more
useful to local users.
Distributed data processing system a number of computer systems are linked together. So the
facilities available-in one computer system can be shared by all. This link is called computer network.

GENERATIONS OF COMPUTERS

  The history of computer development is often discussed with reference to different

generations of computing devices. In computer terminology, the word generation is described as
a stage of technological development or innovation. A major technological development that
fundamentally changed the way computers operate resulting in increasingly smaller, cheaper,
more powerful and more efficient and reliable devices characterize each generation of
computers.

1. First Generation (1940-1956):Vacuum Tubes

First generation computers were vacuum tube / thermionic valves-based machines. These
computers used vacuum tubes for circuitry and magnetic drums for memory. A magnetic drum
is a metal cylinder coated with magnetic iron-oxide material on which data and programs can be
stored. Input was based on punched cards and paper tape, and output was displayed on printouts.
First generation computers relied on binary-coded language (language of 0s and 1s) to
perform operations and were able to solve only one problem at a time. Each machine was fed
with different binary codes and hence were difficult to program. This resulted in lack of
versatility and speed. In addition, to run on different types of computers, instructions must be
rewritten or recompiled.

 Examples: ENIAC, EDVAC, and UNIVAC.

Characteristics of first generations computers:

• These computers were based on vacuum tube technology.
• These were the fastest computing devices of their times. (computation time was in milliseconds)
• These computers were very large, and required a lot of space for installation.
• Since thousands of vacuum tubes were used, they generated a large amount of heat. Therefore, air conditioning was essential.
• These were non-portable and very slow equipments.
•  The lacked in versatility and speed.
• They were very expensive to operate and used a large amount of electricity.
• These machines were unreliable and prone to frequent hardware failures. Hence, constantmaintenance was required.
• Since machine language was used, these computers were difficult to program and use.
• Each individual component had to be assembled manually. Hence, commercial appeal of these computers was poor.

2. Second Generation Computers (1956-1963):Transistors

In the sixties, there was lot of development in semiconductor field - a field of materials. In
vacuum tubes, a filament is heated to emit electrons,(the basic component of an atom)that carry
current. In 1946,Willam Shockley and a few of his colleagues invented transistors, which do not
need any heating to liberate electrons in addition to being smaller in size, they saved power due
to the absence of heating and hence the cooling needed. the smaller size resulted in smaller
distances that the electrons have to travel to transmit information from one part of the computer
to another. Hence calculations became faster. The reliability also increased. Today you cannot
see any second generation computers.
The smaller size of components saw mass production of computers which became
cheaper. Many companies started buying and using them increasing the demand. Computer
programming languages developed further to make programming easier and user friendly. yet if
you compare today’s computers, they were a lot behind. The increased use of computers and the
consequent mass production sent the prices crashing down. Computer scientists and electronic
engineers were developing more sophisticated computers.

Characteristics of second generation computers:

• These machines were based on transistor technology.
• These were smaller as compared to the first generation computers.
• The computational time of these computers was reduced to microseconds form milliseconds.
• These were more reliable and less prone to hardware failure. Hence, such computer required less frequent maintenance.
• These were more portable and generated less amount of heat.
• Assemble language was used to program computers. Hence, programming became more time efficient and less cumbersome.
• Second generation computers still required air conditioning.
• Manual assembly of individual components into a functioning unit was still required.

 3. Third Generation Computers(1964 - early 1970s):Integrated circuits

In second generation computers, one could recognize the circuit components such as
transistors, resistors and capacitors distinctly. There were physically separate or “discreet”.
Slowly scientists started integrating these components together so that they are not separate.
They were fused into the circuits. People called it large scale integrated circuits (LSI).
Computers using such components were called third generation computers. Since components
were packed together more densely, the size of computers became smaller. Programmers also
developed more sophisticated software. By 1970, engineers developed a device called
microprocessor. Lot of circuits was packed into it. Intel 4004 was one such chip.

Characteristics of third generations computers:

• These computers were based on integrated circuit (IC) technology.
• They were able to reduce computational time from microseconds to nanoseconds.
• They were easily portable and more reliable than the second generation.
• These devices consumed less power and generated less heat. In some cases, air conditioning was still required. 
• The size of these computers was smaller as compared to previous computers. 
• Since hardware rarely failed, the maintenance cost was quite low. 
• Extensive use of high-level languages became possible.
• Manual assembling of individual components was not required, so it reduced the large requirement of labour and cost. However, highly sophisticated technologies were required for the manufacture of IC chips.
• Commercial production became easier and cheaper.

4. Fourth Generation Computers (Early 1970s – till date):Micro processors

More and more circuits were packed in a microprocessor. The components were
integrated further and very large scale integration (VLSI) technology revolutionized computer
field further. Intel Corporation made chips such as 8080 and 8086 to be followed by 80286,
80386, 80486 and now the Pentium processor. These chips perform calculations faster. They are
not only used in computers, but also in measuring devices and even in house hold devices such
as washing machines.
Computers using such VLSI chips progressively shrunk in size. Computers using the
microprocessors are termed as microcomputers. The software technology also developed further.
Programmers developed more sophisticated and user friendly software. In course of time, the
cost of these computers have come down so much that even individuals bought them so they
came to be known as personal computers.

Characteristics of Fourth generation computers:

• Fourth generation computers are microprocessor-based systems.
• These computers are very small.
• Fourth generation computers are the cheapest among all the other generations.
• They are portable and quite reliable.
• These machines generate negligible amount of heat, hence they do not require air conditioning. 
• Hardware failure is negligible so minimum maintenance is required. The production cost is very low.
• GUI and pointing devices enable users to learn to use the computer quickly.
• Interconnection of computers leads to better communication and resource sharing.

5. Fifth Generation Computers (Present and beyond):Artificial Intelligence

Up to fourth generation, the classification was based purely on hardware. Fifth generation
computers are classified based on software also. VLSI technology is used in fifth generation
computers. They have large main memories. The speed is also high. In addition to all this, Fifth
generation computers run software called ‘expert systems’.

Characteristics of Fifth Generation computers:

Mega Chips:
Fifth generation computers will use Super large Scale integrated (SLSI) chips, which will
result in the production of microprocessor having millions of electronic components on a single
chip. In order to store instructions and information, fifth generation computers require a great
amount of storage capacity. Mega chips may enable the computer to approximate the memory
capacity of the human mind.

Parallel Processing:
Most computers today access and execute only one instruction at a time. This is called
serial processing. However, a computer using parallel processing accesses several instructions at
once and works on them at the same time through use of multiple central processing units.

Artificial Intelligence (AI):
It refers to a series of related technologies that tries to simulate and reproduce human
behaviour, including thinking, speaking and reasoning. AI comprises a group of related
technologies: expert systems (ES), natural language processing (NLP), speech recognition,
vision recognition, and robotics.