System Case Form Factors
Theform factorof a PC case defines its style, size, shape, internal organization, and the
componentsthatarecompatiblewithcasesofthatformfactor.Computerformfactorsde-
fine a general standard for compatibility for the system case, the motherboard, the power
supply, the placement of I/O (input/output) ports and connectors, and other factors.
The three most popular types of case form factors are: Baby AT Though virtually obsolete by today’s standards, the Baby AT
form factor is still considered popular because of its very large installed base
stemming from its popularity in past years. The Baby AT is a smaller version
of the AT form factor that is narrower in width, but otherwise shares the AT
form factor’s dimensions. Baby AT power supplies and motherboards are
backward-compatible with AT cases, but the reverse is not true. AT power
supplies and motherboards will not fit into Baby AT cases. Because of its
smaller footprint, the Baby AT soon became preferred over the AT form
factor. The Baby AT form factor is used for desktop and tower configurations.
ATX Intel developed this form factor in the mid-1990s and it has become the de
facto form factor for motherboards and system cases. All Pentium-based systems
require motherboards and chipsets that use the ATX form factor specification.
This, and the fact that most new systems are using ATX, accounts for why
the ATX form factor is so popular. ATX is actually a family of form factors
and has replaced the Baby AT form factor as the de facto standard for PC cases,
motherboards, and especially power supplies (many form factors, such as NLX,
do not define a power supply). Because ATX is generally compatible with Baby
AT, many users are now upgrading to this form factor. Other form factors in
the ATX family are the slightly smaller MiniATX motherboard specification,
the slightly larger Extended ATX motherboard specification, and other smaller
specifications, such as the MicroATX and the FlexATX
NLX The NLX form factor, which is also called Slimline form factor, is quickly
becoming the new standard for mass-produced desktop systems because it offers
manufacturers more flexibility and room for future advancement. The NLX has
been established as a true form factor standard. Many experts are predicting
the NLX, which is used for both desktop and tower PCs, will become the most
popular form factor in the future.Herearesomeoftheotherformfactorsthathavebeenorareinuseforsystemcases: PC XT This form factor was used for both the original IBM PC and its
successor the PC XT. When the IBM PC AT was released in 1984, it generally
replaced the PC XT form factor, but PC XT and its clones survived for a few
years. The PC and the PC XT were only available as desktops. The U-shaped
case was made of heavy-gauge steel and was fastened on the rear of the PC
and removed over the front of the case. The power supply had 130 watts
(only 63.5 watts on the PC) and was located at the rear of the case with a
power switch that protruded through a cutout on the case.Chapter 15: The System Case^357