Data Communications

           Data Communication is the process of moving information from one point to another by means of some transmission system.

Network

          A network is a collection of entities that exchange information or good. Few examples of networks are railway system, nervous system of animals, telephone system.

Communications Network

          A communications network is a system of interconnected computers, and communication devices that can communicate with one another and share resources. At the most elementary level, a computer network consists  of two computers connected with each other by a cable to allow them to share data. A device connected to a network is called a node. A node may be a device such as a computer, a printer, workstation etc.

Advantages of Networks

         Networks offer several advantages over stand along systems. Some of these advantages listed below:

• Sharing of peripheral devices: Expensive resources can be shared by connecting them to the network.

• Sharing of programs and data: Some programs may be expensive, and it may not be possible to purchase multiple copies. Such programs can be shared a network.

• Better communications: Networks can be used to establish communication such as e-mail.

• Access to databases: Users can access numerous databases by making them available on the network.

Common Network Elements

            The different types of components that you can find in a network are:

• Servers: Computers that provide shared resources to the network users.

• Clients: Computers that access shared network resources provided by the users.

• Communication Media: The media through which data is being transmitted.

• Network Operating System: Software that manages the activities of a network.

• Shared resources: Any service or resource made available for use by the members of the network.

• Modem: Used to connect a computer to another computer over phone lines.

• Hub: A hub can be thought of as a junction box, permitting new computers to be connected to a network as easily as plugging a power cord into an electrical socket. Hubs are commonly available in 4, 8, 16 port sizes, enabling anywhere from 4 to 16 network devices to be plugged into a network. There is no need to connect all the ports of a hub to network devices simultaneously. When no cables are plugged in, the signals bypass the unused ports. Some hubs have an additional interface port that connects to another hub, increasing the size of the network.

• Switch: An enhanced version of the hub. Typically a switch can distribute the communication load so all the computers connected to the switch can communicate effectively.

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Application Software

               Application software is designed to perform useful general-purpose tasks. For example, an application program called Solitaire is a single program that lets you play a card game. Application software can be grouped as customized software or as application packages. Customized software is generally designed for a particular customer whereas application packages are "off the shelf" programmes designed for the general public. Common types of application software are:

• Word Processing
• Spreadsheet
• Database Management System
• Presentation Software
• Desktop Publishing and Graphic Design
• Web Design and Development

Device Drivers

               Virtually every hardware component located inside or connected externally to a computer requires associated software component to enable that hardware to communicate and function with the operating system, other applications and other hardware components of the computer. This software component is referred ti as driver software of that hardware component. Until you install the proper software derive for a hardware component that hardware component remains logically isolated from the rest of the components of the computer.



Booting the Computer

            The process of loading the operating system into the computer's main memory from the hard disk, floppy disk or CD is called booting. A programme known as the boot routine or bootstrap loader is in change of the booting process and this boot routine is stored permanently in the computer's electronic circuitry, typical in ROM. Another series of programmes which start up prior to the booting process are the diagnostic routines. These programs test the main memory, the CPU and other parts of the system to make sure that they are running properly.



System Start up Process

            When you switch on a computer it automatically loads a program called the Basic Input / Output System (BIOS). The BIOS is stored on a special chip on the computer's motherboard. As it runs, it performs a number of essential tests on the computer hardware. These tests are called Power On Self Test (POST).



Software Evaluation

              Software evaluation is the process of checking the software for suitability for the required function. the major steps involved in software evaluation are:

• Identity clearly the problem or application for which the software is required.

• Inspect the manual or instructions supplied with the software.

           - Is the manual clearly written? 

           - Does it explain the main functions of the software? 

           - Does it provide examples?

• Input / Output Interfaces

             - Do the input and output of the software meet your requirements?

• Test the system with your own data sets to see its performance.

• Reliability

              - Is the system consistent? 

              - Does it give consistent answers to similar or the same problems?

• User Friedliness

              - User interface is easy to use. 

              - Error message are clear. 

              - Time periods to wait between successive screens are acceptable.

• Adaptability

              - To what extent the original problem be modified without affecting the functionality of the software.

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System Software

Software

          Software refers to instructions which are used by  the computer to perform various tasks. The word programme is synonymous with software. Software is created with programming languages and related utilities. Software is generally classified into two types: System Software and Application Software.

System Software

          System software is responsible for controlling, integrating and managing the individual hardware components of a computer system so that other software and the users of the system see it as a functional unit without having to be concerned with the low-level details of the computer hardware.
System software can be further classified as:

• Operating Systems.
• Utilities and service programs.

Operating Systems (OS)

              The Operating System manages the resources and the basic operations of the computer. Without an operating system the computer would not work. The operating system (or a part of it) is loaded into the main memory when the computer is switched on and handles many tasks, which we are unaware of when we use the computer. A part of the operating system remains in main memory until the computer is turned off.

             There are several operating systems used with personal computers such as Windows 98, Windows XP, Linux and Mac OS. Different systems are designed for different hardware platforms or for different functions.

            Operating systems may provide different types of user interfaces such as Command Line Interface and Graphical User Interface (GUI). In the command line interface, users communicate with the operating system by typing commands using the keyboard. One of the main disadvantages of the command line interface is that the user has to memorize the commands exactly.

               In the graphical user interface, a user invokes a command by means of graphical objects shown on the screen and the system translates the user action to the operating system commands and executes them on behalf of the user. The graphical user interface was first developed for Apple Macintosh Computers.

              The general-purpose operating systems are typically supplied on CD-ROMs and must be installed before using the computer. Some computers such as hand held computers come with pre-installed operating systems on the computers' ROM. Such operating systems provide only limited capabilities and are virtually impossible to be upgraded.


Utilities and Service Programs 

             Another category of software is utility software, which is a collection of useful programs that enhance the capabilities of the operating system. These software programmes are designed to perform various tasks. Some examples of utility software are Norton Utilities and Download Accelerator.

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Different Types of Printers

            Many different types of printers are in use today. Two primary technologies used for printing are impact printing and non-impact printing. Impact Printers use a print head containing a number of metal pins which strike an inked ribbon placed between the print head and the paper. The non-impact printers are much quieter than impact printers as their printing heads do not strike the paper.

The Most Common Printer Types Are:

• Dot matrix printers,
• Ink-jet printers,
• Laser printers. 

Dot Matrix Printers

              These printers work by firing a matrix of tiny pins (which are located in the print head), through a ribbon similar to that found on a typewriter. As the head moves across the paper the correct pins are fired out to hit an inked ribbon and form the shape of the character required. The greater the number of pins, the higher the quality of the print. Dot matrix printers are impact printers and are used to print multipart stationery. So print several copies of a document at the same time you will need to use a dot matrix printer. Such printers are cheap and have the lowest running cost compared to any other type of printer.

Laser Printers

            These non-impact printers offer high-speed printing and an excellent quality of text and graphics. A laser beam is used to from an image on a rotating, charged metal drum. This then picks up toner from the toner cartridge and transfers it onto paper. Very soon after wards heat and pressure are applied so the toner sticks to the paper. Since they are page printers they are very fast. Colour laser printers are now available and are mainly used for desktop publishing. Although they are expensive, they are likely eventually to come into widespread use.

Inkjet Printers

             Inkjet printers can produce high quality text and graphics. They are quieter than dot matrix printers. The technology involves ink flowing through the appropriate nozzles (usually in an array of 64) where it is then heated and a bubble is formed. This expands to release a tiny droplet of ink onto the paper.

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Different Types of Display Screens

CRT Monitor

                  A cathode-ray tube and associated electronics connected to the video output of a computer. These have higher resolution than TVs. Lager monitors with high resolution are used for specialized application such as desktop publishing and CAD.

LCD (Liquid Crystal Display) Monitor

               LCDs are screens made from two glass/plastic plates with liquid in between. LCDs are commonly used for calculators and laptop computers, as they are far flatter than is possible with cathode ray screens used in TVs and Standard computer monitors.

Main difference of LCDs as compared with CRT monitors are:

• Takes very little space.
• Small energy consumption.
• Sharp pictures.
• Fairly expensive.
• Limited viewing angle.
• Slower response time.

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Different Types of Output Devices

             Output devices translate information processed by the computer into a form that either humans or other machines can understand. There are a variety of output devices, which can be connected to a computer. Some of the common output devices are explained in the following sections.

Monitor

            The most common form of output is the computer screen. It is more correctly called 'monitor' and sometimes referred to as the visual display or VDU.
             The quality of a computer monitor is based on the following properties:

• Resolution: Resolution is the number of pixels, which the screen can display. A 'pixel' is the 'picture element' and refers to the smallest area of the screen that the computer can change.

• The number of colours: it can display (dependent on the computer as well)

• Radiation output. 

More About Monitors..

Printer

                                                               More About Printers..

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Different Types of Input Devices

Formatting

            Hard disks and Diskettes must be formatted before saving data on them. Formatting can be considered as an initialization process that prepares the disk or diskette electronically so that it can store data or programs.


Input Devices

            Input devices enable data to be fed into the computer in a form that the computer can use. Input devices are categorized into two types: keyboard entry devices and direct entry devices. A devices through which data can be entered to the computer by pressing keys is called a keyboard entry device whereas all the other types of input devices are called direct entry devices.


Keyboard

The keyboard is the most commonly used input device and has been used since computers were first introduced. They are intelligent devices and contain their own chips. Each key is switch, which closes when that particular key is pressed. The microprocessor scans the keyboard hundreds of times a second to see if a key has been pressed; if it has, a code that corresponds to that key is sent to the Processing Unit. The CPU then translates this code into the ASCII code (the code that computers use to represent characters on the computer keyboard), which is then used by the computer program.


Mouse

A mouse is another popular input device that forms an essential part of a computer system. Its movements on the desktop are translated into digital information, which in turn is fed to the computer, causing the cusor to move on the screen. Underneath the mouse there is a ball which rotates when the mouse is moved by the user and sensors pick up this movement. A mouse usually has two or three buttons, and these are used to make selections on the screen. The Mouse is classified as a pointing device. Joysticks, Touch Screens and Light pens are a few other examples for pointing devices.


          A newer type of mouse is the optical mouse. An optical mouse uses a light-emitting diode (LED), an optical sensor, and a digital signal processing (DSP) in place of the traditional mouse ball and electro-mechanical transducer. Movement is detected by sensing changes in reflected light, rather than by interpreting the motion of a rolling sphere.


Digital Camera

              Digital Cameras store the images digitally rather than on film. Digital still cameras can be connected to a computer and the pictures taken on them can be transferred while digital motion cameras or web cams can be used to create video and for video conferencing purposes.

Microphone

            A microphone can be used to record sound into a computer. Microphones are also used for voice communication through a computer, for example, for making telephone calls through a computer.

Scanners

            Scanners are input devices normally used to scan text or pictures. The scans are then stored in a computer's memory where they can then be accessed and modified using a desktop publishing package, before being printed. Both black and white, and color scanners are available.

            Scanners often come with OCR software. Optical Character Recognition (OCR) is where the text on a page is scanned and then converted and fed into a word processing package so that it can be modified according to the needs of the user. OCR software may not recognize certain characters, be they handwritten, typed fonts or symbols.


Other Devices 

           A variety of devices exist which allow people to input different kinds of information into a computer. Some such devices are:

• Fingerprint Reader - Used to capture a fingerprint of a person into the computer.

• Magnetic Ink Character Recognition (MICR) - Used to recognize characters printed in special ink. e.g. on cheques.

• Environment Sensors - Movement, Temperature, Humidity, etc., can be monitored through a computer using these devices.

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Different Types of Memory

Floppy Disk

           A floppy disk or a diskette is a round flat removable piece of plastic coated with a Ferric Oxide layer, and encased in a protective plastic cover, called the disk jacket. The Ferric Oxide layer is capable of holding a magnetic field. Data is stored on a floppy disk by means of a disk drive, which alters the magnetic orientation of the particles in the Ferric Oxide layer. Reading data from a diskette means that the data stored as a magnetic pattern on a diskette is converted to electronic signals and transmitted to the memory of the computer. Writing data on a diskette means electronic information is transformed into magnetic patterns and recorded magnetically on the diskette.

                                              Evolution of Diskettes

Year Introduced	Physical Size (in inches)	R/W Capability	Maximum Capacity	Number of sides used
1970	8	R	100 Kilobytes	Single
1973	8	R/W	250 Kilobytes	Double
1976	5.25	R/W	100 Kilobytes	Single
	5.25	R/W	1.2 Megabytes	Double
1980	3.5	R/W	1.44 Megabytes	Double

Zip disks and Jaz disks

          These disks are very similar to floppy disks except that they can be used to store large amounts of data. Zip disk capacities from 100 to 750 MB and Jaz disks come in 1 and 2GB capacities. Both these disks are removable and portable and provide much better performance than floppy disks.



Magneto optical disk

           Magneto optical disk drives use a combination of a laser, to heat the surface of the disk, and a magnetic head, to record data. While these disks are high performance, they are expensive. Magneto optical disk have capacities ranging from 128 MB to several Gigabytes.

Magnetic Tape

          Magnetic tapes are similar to audio tapes and store data in a serial manner (i.e. data is stored one after the other on the tape). These tapes can store large amounts of data but are primarily used for backup because the access speeds are slow.



CD/DVD

          A Compact Disk (CD) is a plastic disk where disk is optically 'written' on its surface. The data written on the disk is read using a CD-ROM drive which uses lasers for this purpose. Usually once the data has been 'written' (or 'burnt') on to the CD, it is not possible to change it, hence Read Only Memory. Some CDs are re-writable. To 'write' to a CD, a drive called 'CD Writer' must be used. The  faster the CD ROM drive can read a CD, the faster the computer will be able to get data from the CD. Digital Versatile Discs (DVD0 use a similar concept to CDs except that are able to use multiple surfaces on a single disc and so can be used to store larger amounts of data. A typical CD can store 650 to 700 MB of data while a DVD can store from 2GB to 8GB of data.

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