Hardware Reference
In-Depth Information
SFX/SFX12V
Intel released the smaller microATX motherboard form factor in December 1997. At the
same time, it released the small form factor (SFX) power supply design to go with it.
Even so, most microATX chassis continued to use the standard ATX power supply in-
stead. Then in March 1999, Intel released the FlexATX addendum to the microATX spe-
cification, which was a small board designed for low-end PCs or PC-based appliances.
Since then, the SFX supply has found use in many new compact system designs. Unlike
mostofthepowersupplyformfactorspecificationsinwhichasinglemechanicalorphys-
ical outline is defined, the SFX standard actually defines five different physical shapes,
someofwhicharenotdirectlyinterchangeable.Inaddition,therehavebeenchangestothe
connectors required as the specification has evolved. Therefore, when replacing an SFX/
SFX12V-typesupply,youneedtoensureyouarepurchasingthecorrecttype—whichisto
say the type that will physically install in your chassis—as well as have the correct con-
nectors for your motherboard.
The number and types of connectors have changed over the life of the specification. The
original SFX power supply specification included a single 20-pin motherboard connector.
The 4-pin +12V connector to provide independent CPU power was added as an option
in the 2.0 revision (May 2001) and was made a requirement in revision 2.3 (April 2003),
causing the spec to be renamed as SFX12V in the process. SFX12V version 3.0 changed
the main motherboard power connector from 20 pins to 24 pins and made Serial ATA
power connectors a requirement. The current SFX12V version 3.1 was released in March
2005 and contains a few additional minor revisions, including a change to High Current
System(HCS)terminalsintheconnectors.SFX12Vincludesseveralphysicaldesigns,in-
cluding one called the PS3 form factor.
OnastandardSFX/SFX12Vpowersupply,a60mmdiametercoolingfanislocatedinside
the power supply housing, facing the inside of the computer's case (see
Figure 18.2
). The
fan draws the air into the power supply housing from the system cavity and expels it
through a port at the rear of the system. Internalizing the fan in this way reduces system
noiseandresultsinastandardnegative-pressuredesign.Thesystemcanalsouseaddition-
al processor and chassis cooling fans, which are separate from the power supply.
Figure 18.2
SFX/SFX12V standard power supply with internal 60mm fan.
