Most people think of a case as just what holds a PC together. That view is reasonable for people who buy a PC and never open the case, but anyone who builds or upgrades PCs soon realizes that not all cases are created equal. The following sections describe what you need to know about cases.
PC cases are available in a bewildering array of sizes, shapes, and
Form factor is the most important thing
about a case, because it determines which motherboards and which
power supplies fit that case. Cases are available in the following
The 1984 IBM PC-AT introduced the
factor. AT cases accept full-size AT motherboards and
reduced-size Baby AT motherboards. All AT-variant cases have a
circular hole in the rear panel for the motherboard keyboard
connector and knockouts for external DB connectors that mate to
serial, parallel, and other ports present as header pins on AT
motherboards. AT cases have been produced in two variants, which
differ only in the power supply they accept.
Desktop/AT cases use the original AT form factor
power supply, with a paddle switch built into the power supply
Tower/AT cases use a modified AT power supply that instead has four main power leads that connect to a switch built into the case. Desktop/AT cases and power supplies are hard to find nowadays, but Tower/AT cases and power supplies are still readily available. AT cases of either type are a poor choice for building a new system. ...