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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Components of a Computer System

                  By considering the functions performed by various components, a computer can be represented as a collection of logical components as in Figure 1.3. The main hardware components of a modern computer system are the central processing unit (CPU), the main memory, the secondary storage and the In put-Out put devices.

 

System Unit

                  The system unit, or the cabinet houses most of the essential components of the computer system such as the power supply, the motherboard, the CPU chip, specialized chips, the system clock, RAM, ROM, expansion board and bus lines.


Central Processing Unit (CPU)

The central processing unit performs the majority of calculations and controls the operation of a computer. CPUs are rated by the speed at which they can execute instructions. The speed of a CPU is measured in Megahertz (MHz), and is also known as the clock speed. The higher the value of the speed the faster the computer can run programs. The capacity of a Central Processing Unit is expressed in terms of word size. A word is the maximum number of bits that the CPU can manipulate or store at one time.

The CPU consists of two parts: the control unit (CU) and the arithmetic/logic unit (ALU)

Different manufactures are making CPUs today. Some of these popular CPUs available today are the Intel, AMD, Cyrix and Motorola.


Control Unit (CU)

                  The control unit controls and directs the operation of the entire computer system. Although it does perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer. It obtains instructions from the program stored in main memory, interprets the instructions, and issues signals, which cause other units in the system to execute them.


Arithmetic-Logic Unit (ALU)

                  The arithmetic-Logic unit performs arithmetic operations such as addition, subtraction, multiplication and division on data. It also performs logical operations, which involve comparison of data. In microcomputers, the entire CPU is typically fabricated on a single chip.


Motherboard

                  The motherboard is the main circuit board inside the computer. It can be considered as the main communication center through which all the components of the computer transmit data back and forth. All the main parts including the central processing unit of the computer are typically plugged in to the mother board. The mother board also provides sockets, called expansion slots, to plug in special electronic circuitboards to enhance the functionality of the computer. These extra circuitboards are called expansion cards, by using which you can customize a computer to suit your needs. One other major function of the mother board is to supply the necessary power to all its expansion cards.

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Data Representation

             Computers use the two-state system to represent data. Such a two state system is referred to as a binary system. In computers these two states are denoted by the digits 0 and 1 and any such value is called a binary digit or bit. In side the computer these two states are typically implemented by using two different voltages.

             The smallest unit of data that can be stored in a computer is a bit. A bit will have the value '0' or '1' . A large collection of such '0's or '1's is what makes up data in a computer.

Smallest Unit           = 1 bit

8 bits                     = 1 byte (B)

1024 bytes             = 1 kilobyte (KB)

1024 kilobytes        = 1 megabyte (MB)

1024 megabyte       = 1 gigabyte (GB)

1024 gigabyte         = 1 terabyte (TB)
(In computer jargon, One Kilo = 1024)

              The capacity of a particular storage device and the space taken up by a file are always measured using these units.

              Letters, numbers and special characters are represented within a computer by means of a binary coded scheme. Three popular binary coding schemes use eight bits to represent characters whereas Unicode uses 16 bits.

Character	ASCII-8	EBCDIC	Character	ASCII-8	EBCDIC
A B C D E F G H I J K L M	0100 0001 0100 0010 0100 0011 0100 0100 0100 0101 0100 0110 0100 0111 0100 1000 0100 1001 0100 1010 0100 1011 0100 1100 0100 1101	1100 0001 1100 0010 1100 0011 1100 0100 1100 0101 1100 0110 1100 0111 1100 1000 1100 1001 1101 0001 1101 0010 1101 0011 1101 0100	N O P Q R S T U V W X Y Z	0100 1110 0100 1111 0101 0000 0101 0001 0101 0010 0101 0011 0101 0100 0101 0101 0101 0110 0101 0111 0101 1000 0101 1001 0101 1010	1101 0101 1101 0110 1101 0111 1101 1000 1101 1001 1110 0010 1110 0011 1110 0100 1110 0101 1110 0110 1110 0111 1110 1000 1110 1001
0 1 2 3 4 !	0011 0000 0011 0001 0011 0010 0011 0011 0011 0100 0010 0001	1111 0000 1111 0001 1111 0010 1111 0011 1111 0100 0101 1010	5 6 7 8 9 ;	0011 0101 0011 0110 0011 0111 0011 1000 0011 1001 0011 1011	1111 0101 1111 0110 1111 0111 1111 1000 1111 1001 0101 1110

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