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.