Power Supplies - Upgrading and Repairing PCs - page 1067

Note
Althoughtwopowersuppliescansharethesamebasicdesignandformfactor,theycandiffer
greatly in quality and efficiency. Later in this chapter, you'll learn about some of the features
and specifications to look for when evaluating PC power supplies.
More than 10 different power supply form factors have existed that can be called industry
standards. Many of these are or were based on designs IBM created in the 1980s, whereas
the rest are based on Intel designs from the 1990s to the present. The industry-standard
form factors can be broken down into two main categories: those that are currently in use
in modern systems and those that are largely obsolete.
Note that although the names of some of the power supply form factors seem to be the
same as those of motherboard form factors, the power supply form factor relates more to
the system chassis (case) than to the motherboard. That is because all the form factors use
oneofonlytwomaintypesofconnectordesigns:eitherATorATX,withsubtlevariations
on each. So, although a particular power supply form factor might be typically associated
with a particular motherboard form factor, many other power supplies would plug in as
well.
For example, all modern ATX form factor motherboards with PCI Express slots have two
main power connectors, including a 24-pin ATX main connector along with a 4-pin +12V
connector. All the modern power supply form factors include these same connectors and
therefore are capable of plugging into the same motherboards. In other words, no matter
what the form factor of the motherboard (ATX, BTX, or any of the smaller variants of
either), virtually any of the modern industry-standard power supplies will plug in.
Pluggingthepowersupplyconnectorsintothemotherboardisonething,butforthepower
supply to work in the system, it must physically fit inside the chassis or case—and that
is what the different modern power supply form factors are all about. The bottom line is
that it is up to you to ensure that the power supply you purchase not only plugs in to your
motherboard, but also fits into the chassis or case you plan to use.
Tables18.2 and 18.3 showtheindustry-standardpowersupplyformfactors,theirconnect-
or types, and the motherboard form factors with which they are usually associated.
Table 18.2 Modern Industry-Standard Power Supply Form Factors