Chapter 25. Cases

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.

Case Characteristics

PC cases are available in a bewildering array of sizes, shapes, and prices. 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 form factors:


The 1984 IBM PC-AT introduced the AT form 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 itself. 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. ...

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