Hardware Reference
In-Depth Information
the connectors to ensure you get them right. Some systems have a single PS/2 port (some-
times marked in both green and purple) that can be used for either device.
The specifications and related information covering the ATX and related form factors are
available from the Form Factors website at
www.formfactors.org
.
The Form Factors site
providesformfactorspecificationsanddesignguides,aswellasdesignconsiderationsfor
newtechnologies,informationoninitiativesupporters,vendorproducts,andaformfactor
discussion forum.
Note
Somemotherboards,especiallythoseusedinserversystems,comeinnonstandardATXvari-
ations collectively called
extended ATX
. This is a term applied to boards that are compat-
ible with ATX but that are deeper. Standard ATX is 12 inches×9.6 inches (305mm×244mm),
whereas extended ATX boards are up to 12 inches×13 inches (305mm×330mm). Because
technically no official “extended ATX” standard exists, compatibility problems can exist
with boards and chassis claiming to support extended ATX. When purchasing an extended
ATX board, be sure it will fit in the chassis you intend to use. Dual Xeon processors fit in a
standard ATX-size board, so choose a standard ATX-size board for maximum compatibility
with the existing ATX chassis.
microATX
microATX is a motherboard form factor Intel introduced in December 1997 as an evolu-
tion of the ATX form factor for smaller and lower-cost systems. The reduced size com-
pared to standard ATX allows for a smaller chassis, motherboard, and power supply,
thereby reducing the cost of the entire system. The microATX form factor is also
backward-compatible with the ATX form factor and can be used in full-size ATX cases.
Of course, a microATX case doesn't take a full-size ATX board. This form factor has be-
come popular in the low-cost PC market. Currently, mini-tower chassis systems dominate
the low-cost PC market, although their small sizes and cramped interiors severely limit
future upgradeability.
The main differences between microATX and standard or Mini-ATX are as follows:
• Reduced width motherboard (9.6 inches [244mm] instead of 12 inches [305mm] or
11.2 inches [284mm])
• Fewer I/O bus expansion slots (four maximum, although most boards feature only
three)
• Smaller power supply optional (SFX/TFX form factors)
The microATX motherboard maximum size is only 9.6 inches×9.6 inches (244m-
m×244mm) as compared to the full-size ATX size of 12 inches×9.6 inches (305m-
