Hardware Reference
In-Depth Information
system manufacturers and builders to abandon BTX and revert to the more popular ATX-
basedformfactors.OtherlargemanufacturerssuchasHPneverjumpedontheBTXband-
wagon, instead staying with ATX-based systems. Because of the lack of BTX compon-
ent popularity and other problems, I recommend avoiding BTX systems and components
such as motherboards and chassis because they will be difficult to upgrade or replace in
thefuture.ATXremainsbyfarthemostpopularandrecommendedformfactorforsystem
builders and upgraders.
ATX and Other Modern Form Factors
The following sections cover the industry-standard form factors, including ATX, that are
popular on modern systems.
ATX
The ATX form factor was the first of a dramatic evolution in motherboard form factors.
ATX is a combination of the best features of the Baby-AT and LPX motherboard designs,
with many new enhancements and features thrown in. The ATX form factor is essentially
aBaby-ATmotherboardturnedsidewaysinthechassis,alongwithamodifiedpowersup-
ply location and connector. The most important thing to know initially about the ATX
form factor is that it is physically incompatible with either the previous Baby-AT or the
LPX design. In other words, a different case and power supply are required to match the
ATX motherboard. These case and power supply designs have become common and are
found in most new systems.
Intel initially released the official ATX specification in July 1995. It was written as
an open specification for the industry. ATX boards didn't hit the market in force until
mid-1996, when they rapidly began replacing Baby-AT boards in new systems. The ATX
specification was updated to version 2.01 in February 1997, 2.03 in May 2000, 2.1 in
June 2002, and 2.2 in February 2004. Intel publishes these detailed specifications so oth-
er manufacturers can use the interchangeable ATX design in their systems. The current
specifications for ATX and other current motherboard types are available online from the
Desktop Form Factors site:
www.formfactors.org
. ATX is the most popular motherboard
formfactorfornewsystemsandwillcontinuetobepopularinthefuture.AnATXsystem
will be upgradeable for many years to come, exactly like Baby-AT was in the past.
ATX improved on the Baby-AT and LPX motherboard designs in several major areas:
•
Built-in double high external I/O connector panel
—Therearportionofthemother-
board includes a stacked I/O connector area that is 6 1/4 inches wide by 1 3/4 inches
tall. This enables external I/O connectors to be located directly on the board and min-
imizes the need for cables running from internal connectors to the back of the case as
with Baby-AT designs.
