All the popular PC power supply formfactors up through 1995 were based on one of three IBM models, including thePC/XT, AT, and PS/2 Model 30. In the PC market, IBM originally defined the standards, and everybody elsecopied them. Having interchangeable parts means that we have abetter range of choices for replacement items, and the competition makes forbetter pricing, too.
If you can't tell already, I am a fan of the industry-standard formfactors! Having standards and then following them allows us to upgrade andrepair our systems by easily replacing physically (and electrically)interchangeable components. In addition, the powersupply is unique to the system and available only from the originalmanufacturer. Going the customroute means additional time and expense for development. Choosing the former meansthat a virtually inexhaustible supply of inexpensive replacement parts will beavailable in a variety of quality and power output levels.
When designing a PC, theengineers can choose to use one of the popular standard PSU (power supply unit)form factors, or they can elect to build their own. Items that share a form factor are generally interchangeable, atleast as far as their sizes and fits are concerned. The shape and general physical layout of a component is called the formfactor.
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