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[ The PC Guide | Systems and Components Reference Guide | Power | The Power Supply | Power Supply Specifications and Certifications ]

Physical Specifications

In this section we will take a brief look at the physical specifications normally listed for a power supply. These are the routine matters of how the power supply is physically situated, and what the characteristics are of its physical pieces. Nothing fancy here.

Form Factor: The form factor of the power supply. Occasionally, you will see a power supply specified as a form factor that is actually that of the case in which it normally fits. The most common case of this would be a "microATX" power supply. In fact, there is no such power supply form factor; they mean an SFX power supply, which is what normally goes into a microATX system.

Dimensions: The physical dimensions of the case. Normally these are specified as W (width) x D (depth) x H (height). May be given in inches (in) or millimeters.(mm). One inch is 25.4 mm. The standard sizes for the various power supplies are shown in the table on the form factor comparison page.

Weight: The weight of the power supply, in pounds (lb) or kilograms (kg). One pound is 0.4536 kg.

Motherboard Connectors: The number and type of connectors used to interface the power supply to the motherboard. Normally the manufacturer will not say if the connectors are of the AT, ATX, SFX or WTX varieties; you will have to deduce this from the form factor specifications, and from looking at the number of pins listed for each connector. In the case of ATX, SFX or WTX styles, the manufacturer should indicate which, if any, of the optional or auxiliary connectors is provided.

Drive Connectors: The number of drive connectors provided as standard equipment with the power supply, as well as how many of them are the larger "D-shape" type, and how many are the smaller "mini-plug" type. Bigger supplies, as well as those of higher quality, provide more connectors.

Fan Characteristics: Characteristics of the power supply fan that you want to know before purchasing the power supply. Some specs on the fan are commonly provided on spec sheets, but many are not: For example, most manufacturers do not say explicitly whether ATX power supplies blow into the case or out of it. You will have to figure this out from the illustration, or ask them. Here are some items you may see listed:

  • Fan Size: Size of the power supply fan, usually given in mm. Fans are normally square, and this is the nominal length of one side of the fan. (Sometimes the thickness of the fan is also specified, but usually not.)
  • Fan Bearing Type: Whether the fan's motor uses sleeve or ball bearings. See the discussion of the power supply fan to understand why this matters.
  • Voltage: The voltage used to power the fan. If not specified, the default is +12 V.
  • Capacity: How much air the fan can move, usually specified in CFM (cubic feet per minute). Larger numbers are better and mean the fan has more cooling power.

Next: Environmental Specifications

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