Parts Of A Computer and their functions (What they do , how they work ?)

Parts Of A Computer  and their functions

A computer system is made up of hardware and software. Hardware means the physical parts of the computer and software Shears the computer programs that are run on the computer. 

The hardware of a computer is classified into three categories --

1. Input Device 

2. Processing Unit, and 

3. Output Devices 

INPUT DEVICES  :

1. KEYBOARD 

The keyboard resembles a typewriter. But there are addmonal keys that handie control functions. The computer keyboard has three categories of keys—~ 

1. Alphanumeric keys 
2. Special Keys
3.  Function Keys

The Alphanumeric Keys:

The Alphanumeric Keys comprise alphabets (A-Z or a-z) ,Numbers (0-9) and other characters like space.  .  /  > < ' " ;  :  ~ @ # $ % ^ & * ( ) + | \ { } [ ] . 

The Special Keys :

The Special Keys perform specific tasks. Some of the special” keys are Enter or the Return Key, Backspace Key, Del Key, the Ins Key, Shift Keys, e Caps Lock Key, Num Lock Key, Ctrl Key and the Alt Key. 

The Shift Key

The Shift Key alters the meaning of a  character key, which is depressed at the same time

The Control Key

The Control Key generates control functions while the Alt + Key often gives graphics characters. 

The Esc Key 

The Esc Key is generally used to signify that the current program is no longer required. The program would return the control to an earlier, master program allowing the user to choose again, 

Cursor keys

Cursor keys are supplied to move the  cursor about the screen. The cursor is a symbol displayed on the screen at the - Higa position where the next character is to be keyed in, edited, altered or deleted. 

The-Function Keys:

The-Function Keys are used to perform a set of operations by a single keystroke. The function keys can be used for various functions. They can be used as shorthand for a sequence of keystrokes, configured accordingly. 

 2. MOUSE 

Another input device for terminals or microcomputers is mouse. Used as a pointing device, the mouse is a small box, about the size of a tape cassette with a round track ball on the bottom and one or more buttons on the top. The mouse is attached to a terminal or microcomputer by a cable. When the user rolls the mouse across a flat surface, the screen cursor moves in the direction of the mouse’s movement (this movement ts measured in hundredths of an inch). \f the user rolls the mouse forward and to the right; the cursor moves up and to the right on the screen. Such movements enable the user to 

i). Point to icons or tiny pictures that identify processing choices. 

ii).  Point to items in lists. 

iii).  Draw lines and pictures on a screen. !

With proper software mouse can be used to draw pictures and edit text. 

3.  JOYSTICK 

Joysticks are designed in the P) shape of handles that swivel in 360degree arcs. This enables their users to control the screen figures. Joysticks are mostly used to play games and control presentation graphics. 

 OUTPUT DEVICES :

1. THE VISUAL DISPLAY UNIT 

The Visual Display Unit (VDU) is used for interactive processing /.@., data that is being keyed in is displayed on the screen or monitor. Messages and processed information are also displayed on the screen. The combination of keyboard and the VDU is usually referred to as Video Display Terminal (VDT), which is an input / output (I / 0) device. 

Most VDU monitors use a cathode ray tube (CRT) that looks like a television picture tube. The depression of a key on the keyboard causes binary code to be generated, which identifies the key. T he information typed goes to the memory unit of the VDU, which is used to refresh the display. The display is refreshed at a minimum of 50 cycles per second ’ to avoid a flicker. 

The characters are keyed into the memory of the VDU and then, on depression of the RETURN key, the entire contents of memory, or selected parts, are transmitted to the computer. 

The video controller controls the formation of images. The video controller along with the memory is termed as the display adaptor. | 

Most existing display adaptors are designed to display alphanumeric data and are used to enter and retrieve letters, numbers and special characters in the text mode. 

However, in the graphics mode the display screen can be divided (or “mapped") into thousands of picture elements or pixels on or off. The processor draws a graphic image (may be a part of text) displayed in multiple typefaces and type styles, or it may be a drawing. 

The number of dots (pixels) on the screen is the measure of resolution of the monitor .

For display of characters, the screen js divided into a matrix of rows and columns with each cell in the matrix being used 

for one character. Typically, 8O character positions .are provided on one line with 20 to 25 lines on the screen. 

Display adaptors are of various types and are normally classified on the basis of resolution, color and display mode. 

 MGA (Monochrome Graphics Adaptor)

Monochrome Graphics Adaptor [MGA]. The term graphics is a misnomer since the device supports text only. Although the option is monochrome or single color, it offers various  attributes e.g. the brightness and intensity of characters which can be changed .

CGA (Colour Graphics Adaptor)

Colour Graphics Adaptor supports both text and graphics mode. It functions in color and monochrome modes in various resolutions. Tha CGA works with different types of monitors. However ib gives poor display quality in the text mode. The typical resolution is'640 * 200 {i.e., 640 rows. * 200 columns) in the graphic mode. 

  HGA (Hercules Graphics Adaptor)

 Hercules Graphics Adaptor is a monochrome adaptor with an additional graphics display mode which provides high’ resolution monochrome graphics. In text mode it functions like MGA, but in the graphics mode it offers a resolution of  750 * 350 dots, even better than the CGA. In the graphics mode the HGA has no colour although it offers brightness and intensity variations. 

EGA (Enhanced Graphics Adaptor)

 Enhanced Graphics Adaptor was developed in an effort to unify the variety of display adaptors. The EGA combines all the features of other adaptors and provides higher resolutions using higher quality color monitors. The EGA supports 16 colours at a time.

  VGA 

Video Graphics Array supports 206 colors at a time with a high resolution. 

2. PRINTERS 

The result of processing could be written by the computer into a tape or a disk, to be used later oF to be given to another Computer as input. However the most common form of computer output is printed output - also called hard. opy. output. Printers are Classified by how they print & and how fast they operate. 

CHARACTER PRINTERS 

Character printers print one character at a time and are used for low-volume printing jobs. 

The technique used to print characters varies widely. Impact printers operate like a typewriter, pressing a typeface against paper and inked ribbon. Impact printers often use a daisy wheel or a dot matrix printing mechanism. 

DOT MATRIX PRINTER 

The dot matrix printer is a versatile low cost device capable of printing in various languages, printing letters of various types, in bold, italics or underlined. It can also be used to print graphics. 

In the dot matrix printer an arrangement of tiny hammers strikes to produce the desired characters. Each hammer prints a small dot on the paper to form the characters. Up To 180 characters per second can be printed. However print quality is not s0-good. Also, the printer is not suited to heavy duty continuous printing.

The printer quality can be improved by setting the printer in ‘double strike mode’ where each character is printed twice with the second printing displaced slightly with respect to the first. This improves the print quality to ‘near letter quality ' (NLQ). Printing in NLQ mode reduces the speed of printing. 

DAISY WHEEL PRINTERS 

In the daisy wheel printer each “petal” of the wheel has a character embossed on it. A motor spins the wheel rapidly and when the desired.character spins to the correct position, a print hammer strikes it to produce the output. 

Daisy wheel printers usually give a better quality of print, but are more expensive than dot matrix printers. Daisy wheel printers can be used to draw simple graphics. The daisy wheel printer has a speed of 90 cps (characters per second). |

There are also a variety of non-impact character printers available.

 INK JET PRINTERS 

Droplets of ink are electrically charged after leaving a nozzle. The droplets are guided to the proper positions on the paper by electrically charged deflection plates. Print quality is good because each character is formed by dozens of ink dots. Text and graphics produced are of better quality and the printer is comparatively fast. They also have the ability to use multiple nozzle print heads, thus enabling it to print in several colors. 

 LINE PRINTERS 

Line printers use impact methods to print one line at a time. The line printer composes one line at a time /.e., the character to be printed in each position is known to the printer before it prints the line. The hammer for the position | is activated whenever the needed character passes under it. A line is thus not necessarily printed from left to right. Line printers normally print 132 characters per line. 

Line printers can print between 300 to 3000 lines per minute. Some are dot matrix devices, but typically use rapidly moving chains or bands of print characters or a print drum to print lines of information paper.

 LASER PRINTERS

Laser printers are page printers. ‘One page of text or pictures is composed at one time . A laser printer utilizes a laser beam that sensitizes selected areas on a’print page. The laser exposed areas attract a toner (an ink powder) that attaches itself to the laser generated charges on the drum. The toner is then permanently fused on the paper with heat or pressure. The resolution of print image is 300 to 1200 dots per inch. 

The printer besides being fast also produces a high quality print. tt can handle large volumes of printed output. Printing is not only limited to lettered text - pictures, graphical displays and other special visual effects are possible. Laser printers are relatively quiet. 

Laser printer can print upto 120 pages (20,0000 lines) per minute. The printers used for typesetting and publishing can print upto 20,000 pages per minute. Laser printers are very expensive. 

PRINTER BUFFER 

Printing takes time  and often the CPU is idle while the printing process takes place. techniques of spooling or printer buffer are used to optimize CPU resources. 

 SPOOLING 

SPOOL - Simultaneous Peripheral Operations On-Line 

Using the spooling technique output is not directly transferred to the printer. The output is first transferred to an ‘intermediary storage medium, such as a disk file. Outputs can be stored in separate files and printed out at a later stage as time and resources permit. 

Printer buffer : The CPU-transfers print output to memory called a “buffer”. The printer then accesses this information and prepares one or more lines of printed output. During this time the CPU performs other tasks. When all the information is printed, the CPU refills the buffer with more data. Some printers contain built-in buffers. 

 PLOTTERS 

While it is possible to use dot matrix and daisy wheel printers for graphics output, the resolution of these devices is limited. The graphic plotter can be used for high quality diagrams. - 

A pen is mounted on an arm moved by motors along the paper up or down to make contact with the paper. Positioning is done by the computer in the form of xy coordinates. Different types of plotters use either a combination of paper and pen movements or only the pen moving on a fixed paper. The unit of movement is an increment. The pen can be moved by increments as small as a thousandth of an inch. Color plotters use four or more pens. Plotters plot.an entire drawing at a rate of several inches per Second with a resolution of a few thousandths of a so a - inch. 

There are two main types of plotters 

i ). Flatbed plotters 

ii). Drum plotters 

FLATBED PLOTTERS 

These use a bed or tray to hold a paper in a fixed position. A single ‘arm moves the pen both horizontally (i.e., x-coordinate) and vertically (i.e., y-coordinate). The computer instructs the flatbed plotter by directing the pen to xy positions on the page .

DRUM PLOTTER 

The paper is mounted on a.drum which rotates back and forth to move the paper along its length as required. Sprocket holes along the paper and on the drum ensure alignment. The pen moves along the width of the paper. _ Thus the pen can draw in any vertical direction. Any type of diagonal line is drawn by combining a horizontal movement of the pen arm with a vertical page movement via the drum. 

Flatbed plotters allow a smaller increment to be employed and thus produce more accurate drawings than the drum type. 

A further advantage of the flatbed type is that it can produce large drawings. 

The accuracy of the drum type depends on the paper transport mechanism, which in turn ig dependant on the width of the paper.