Main computer system

1. Monitor
The monitor shows information on the screen when you type.This is called outputting information. When the computer needs more information it will display a message on the screen, usually through a dialog box. Monitors come in many types and sizes. The resolution of the monitor determines the sharpness of the screen. The resolution can be adjusted to control the screen's display.

A computer monitor image is made up of pixels(dots). In general, the higher the resolution, the better the image. The smaller the dots pitch (typically from 0.25mm to 0.31 mm), the better the image.

Most desktop computers use a monitor with a cathode tube or liquid crystal display. Most notebooks use a liquid crystal display monitor.

To get the full benefit of today's software with full colour graphics and animation, computers need a color monitor with a display or graphics card.

2. Keyboard

The keyboard is the main input device for text and commands. There are many different keyboard layouts and sizes with the most common for Latin based languages being the QWERTY layout (named for the first 6 keys). The standard keyboard has 101 keys. Notebooks have embedded keys accessible by special keys or by pressing key combinations (CTRL or Command and P for example). Ergonomically designed keyboards are designed to make typing easier. Hand held devices have various and different keyboard configurations and touch screens.

3. Speakers

Speakers giveout information in the form of sound. They range widely in quality and price. They are typically packed with computer systems in small plastic boxes with mediocre sound quality. The internal amplifiers requires an external power source, known as 'wall-wart'.

4. Mouse

Most modern computers today are run using a mouse controlled pointer. Generally if the mouse has two buttons the left one is used to select objects and text and the right one is used to access menus. If the mouse has one button (Mac for instance) it controls all the activity and a mouse with a third button can be used by specific software programs. One type of mouse has a round ball under the bottom of the mouse that rolls and turns two wheels which control the direction of the pointer on the screen. Another type of mouse uses an optical system to track the movement of the mouse.

5. System Unit

A system unit, also known as a base unit, is the main body of a desktop computer, typically consisting of a plastic enclosure containing the motherboard, power supply, cooling fans, internal disk drives, and the memory modules and expansion cards that are plugged into the motherboard, such as video and network cards.

6. Printer

The printer takes the information on your screen and transfers it to paper or a hard copy. There are many different types of printers with various levels of quality. The three basic types of printer are:

(i)Dot matrix printers:
Dot matrix printers work like a typewriter transferring ink from a ribbon to paper with a series or 'matrix' of tiny pins.

(ii)Ink jet printers:
Ink jet printers work like dot matrix printers but fires a stream of ink from a cartridge directly onto the paper.This type of printer is the most economical for colour output.

(iii)Laser printers:
Laser printers use the same technology as a photocopier using heat to transfer toner onto paper. The speed of a laser printer is typically abouut 8 ppm (page per minute).

*The information above are sourced from:
(i) http://www.grassrootsdesign.com/intro/hardware.php
(ii) http://en.wikipedia.org/wiki/System_unit