The system case, at its most basic, is a box made of steel or aluminium, the former often covered with plastic, that houses all the electronics that comprise your computer. It will have a power on switch and may also have a reset switch. Probably it will have a couple of lights on the front panel, one indicating the power on status and the other displaying hard disk activity. Normally there will be a vent at the front for air to pass into the case and another vent at the rear for air to pass out. At the front there will be positions for mounting optical drives (CDs/DVDs), floppy drives (getting less common) and card readers (getting more common).
There are a number of distinct physical formats that cases come in, but the most commonly encountered format in the home is the midi-tower which stands vertically. Though less common, you may have a desktop case which sits horizontally on the desk. Also starting to appear in the market are small format cases such as the Shuttle series.
The purpose of the case is threefold. First it provides a structural framework in which all other components can be mounted. Secondly it provides protection to the sensitive components that make up your PC from electrostatic discharge and from physical damage (imagine the damage your cat might do if he got access to the computers innards!). Finally it provides correct ventilation for the removal of the often considerable heat that modern PCs generate. Without this heat removal the PC would overheat and fail.
To get inside a typical midi-tower case normally involves removing a couple of screws at the rear of the case that hold the side panel in place. Once these are removed the side panel generally just slides off.
The picture at left shows an empty midi-tower case with the side panel removed and before any of the electronic components have been fitted. While a lot of midi-tower system cases may look different on the outside, they all conform to a standard, known as the ATX standard, on the inside. This standard ensures that all power supplies that conform to the ATX standard will fit the case, and that the mounting points for the system motherboard are all in specified positions. There is a standard location in the system case for most of the electronic components that make up your PC. With reference to the picture on the left, the power supply unit will be located in the top left corner of the case, the optical drives in the top right, the hard drive(s) in the bottom right and the system motherboard (more on this later) in the main open area.
The rear of the system case is where the sockets on the motherboard emerge, as well as the sockets on any PCI expansion cards or AGP/PCI Express video cards that may be fitted - we'll be covering more on those in future Back to Basics episodes. For now I'll leave you with a picture of the rear of a typical midi-tower system case that has yet to have any internal components fitted.
Next up, the innards.