Often called microcomputers, personal computers prior to 1982 were designed and built by a number of different manufacturers. Aimed at home and small business users, many of these systems provided the first taste of computing for many of today\'s developers and IT managers. However, few of these machines shared common components; for example, a printer designed for one manufacturer\'s computer was not necessarily compatible with another, and all were limited by the technology around which they were based.

It was the 1981 launch of Intel\'s 16-bit 8086 processor that paved the way for the original IBM PC. This computer started to set standards and spawned the imitators that are being built in their millions today. A global industry of manufacturing, support, servicing and training has grown up around the PC.

Although the technologies have changed, the oldest IBM PC and the latest multimedia machine share common principles of operation.

Key Functions of a PC

Before looking at specific PC components, it is worth taking a few moments to consider the key functions that are performed by a computer:

• Input - Entry of raw data; for example, typing names and addresses on a keyboard or transmitting a picture from a digital camera.
• Processing - Manipulation of the raw data to produce useful information, the key purpose of a computer; for example, sorting or indexing the names and addresses or adding effects to the picture.
• Output - Transformation of the data into information, perhaps in a non-computerized format; for example, printing mailing labels from a database or displaying the picture in a brochure
• Storage - Retention of the data until it is needed; for example, filing names and addresses in a database or archiving the picture in an online library. With a basic understanding of these key functions, the role of each of the components of a PC becomes much clearer.

The System Case

The system case is a plastic and metal box that houses components such as the motherboard, disk drives and power supply unit.

System Case Types

There are two basic types of system case: desktop and tower. Both these types are available in different sizes.

Be aware that while a small case may be desirable because it takes up less space, it has less room inside for installing extra devices and is less effective at cooling.

Desktop case

A desktop case is designed to sit horizontally on a surface, so that it is wider than it is long. If turned on its side, a CD-ROM or DVD tray would be oriented incorrectly. These are usually used for office or home PCs. Desktop cases come in two basic sizes: standard and slimline.

Tower case

A tower case is designed to sit vertically on a surface, so that it is higher than it is wide. Tower cases come in three basic sizes: full, midi and mini.

• Full-tower cases are usually used for PC servers - these require the extra internal space for additional hard disks, interface cards and redundant power supply units.
• Midi-tower cases are used for high-end user PCs. These PCs do require extra devices and interface cards, but not as many as a server.

• Mini-tower cases are usually used for office or home PCs where the requirement for additional internal devices and interface cards is limited.