Hardware Reference
In-Depth Information
Note
Some sdmotherboards, especially those used in server systems, come in nonstandard ATX
variations collectively called
extended ATX
. This is a term applied to boards that are
compatible 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 evolution of the
ATX form factor for smaller and lower-cost systems. The reduced size compared 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 become 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 (244mm × 244mm) as
compared to the full-size ATX size of 12 inches × 9.6 inches (305mm × 244mm) or the Mini-ATX
size of 11.2 inches × 8.2 inches (284mm × 208mm). Even smaller boards can be designed as long as
they conform to the location of the mounting holes, connector positions, and so on, as defined by the
standard. Fewer slots aren't a problem for typical home or small-business PC users because more
components such as sound and video are usually integrated on the motherboard and therefore don't
require separate slots. This higher integration reduces motherboard and system costs. External buses,
such as USB, 10/100/1000 Ethernet, and optionally 1394 (FireWire), can provide additional
expansion out of the box. The specifications for microATX motherboard dimensions are shown in
