Hardware Reference
In-Depth Information
Anything that does not fit into one of the industry-standard form factors should be con-
sidered proprietary. Unless there are special circumstances, I do not recommend purchas-
ingsystems based onproprietary boarddesigns. They are difficult toupgrade andexpens-
ivetorepairbecausecomponentssuchasthemotherboard,case,andpowersupplyarenot
interchangeable with other systems. I often call proprietary form factor systems “dispos-
able” PCs because that's what you must normally do with them when they are too slow or
need repair out of warranty.
Obsolete Form Factors
The following sections examine industry-standard motherboard form factors no longer in
use, but which can be commonly found on older systems.
PC and XT
The first popular PC motherboard was, of course, the original IBM PC released in August
1981.
Figure4.1
showshowthisboardlooked.IBMfollowedthePCwiththeXTmother-
board in March 1983, which had the same size and shape as the PC board but had eight
slots instead of five. Both the IBM PC and XT motherboards were 9 inch×13 inch. Also,
the slots were spaced 0.8 inches apart in the XT instead of 1 inch apart as in the PC (see
Figure 4.2
)
. The XT also eliminated the little-used cassette port in the back, which was
supposed to be used to save BASIC programs on cassette tape instead of the much more
expensive (at the time) floppy drive.
Figure 4.1
IBM PC motherboard (circa 1981).
