The modern standalone desktop computer comprises of three main components: the keyboard, the monitor, and the systems unit.

Keyboards have changed progressively since the introduction of the first personal computer in 1981. The designers of the original personal computer decided that it was necessary to include both a typewriter keypad and a numeric keypad on the one keyboard.

Typewriter keypads have a layout that corresponds to that of a typewriter and are generally used for letter writing, memo writing, and the like. Numeric keypads are similar in layout to those found on calculators and are used for rapid entry of numbers.

However, computers also require special keys for moving a pointer, often referred to as a cursor, around the screen. These keypads normally have at least four arrow keys (up, down, left, and right), and several other keys for rapid movement such as page up and page down and home (start) and end.

The designers felt that this was too much for the one keyboard layout so they combined the cursor movement keys in with the numeric keypad where one key is used for two different operations - entering numbers and moving cursors.

To change from one operation to another a special NUM Lock key was provided to switch the keypad into numbers or movement.

This layout was updated with the introduction of the IBM PC-AT in 1985. However, the changes here were only minor and the dual function of the numeric keypad was retained with this model even after loud complaints from users.

With the introduction of the IBM PS/2 in 1987 a new, extended keyboard was introduced where the separate cursor movement keypad was inserted in between the typewriter keypad and the numeric keypad.

The extended keyboard is now the one supplied with mouse personal computers - with the exception of laptop and notebook computers, which need to be more compact. However, the numeric keypad, even on the extended keyboard can still be toggled between numbers and cursor movement.

The monitor or computer screen is sometimes referred to as an output device as it displays data or typing from the keyboard.

Monitor technology has changed greatly over the years. The first screens were monochrome, or single colour, usually green or amber.

The first colour screen was introduced with the IBM PC but it was extremely crude by today’s standards. The first colour computer used the Colour Graphics Adapter (CGA) developed by IBM in 1981. In 1984 the Enhanced Graphics Adapter (EGA) succeeded this and in 1987 the Video Graphics Adapter (VGA) succeeded the EGA adapter. Today we have Super-VGA adapters and even greater screen resolutions.

Generally, most computers today will be in VGA or Super-VGA formats.

Each of these formats provided a crisper, clearer colour image than its predecessor. Since the computer screen is actually made up of tiny dots (much like a picture in a newspaper) the more dots that you have the better the resolution of the picture.

Super-VGA screens have many more dots than a CGA screen.

The third part of the computer is the systems unit - sometimes referred to as the central processing unit (CPU). The system unit really is the computer - it is here where the processing takes place.

Systems units vary immensely. However, most of them have at least one floppy disk drive at the front or side. A series of slots are located at the back with sockets for attaching special cables and devices.