Hardware Reference
In-Depth Information
to the main board, enabling the expansion cards to install sideways. This allows for a slim
or low-profile case design and overall a smaller system than the Baby-AT.
Although Western Digital no longer produces PC motherboards, the form factor lived on,
and many other motherboard manufacturers duplicated the general design. Unfortunately,
because the specifications were never laid out in exact detail—especially with regard to
the bus riser card portion of the design—these boards are termed
semiproprietary
and are
not interchangeable between manufacturers. Some vendors, such as IBM and HP, have
built LPX systems that use a T-shaped riser card that allows expansion cards to be moun-
ted at the normal 90° angle to the motherboard but still above the motherboard. This lack
of standardization means that if you have a system with an LPX board, in most cases you
can't replace the motherboard with a different LPX board later. You essentially have a
system you can't upgrade or repair by replacing the motherboard with something better.
In other words, you have what I call a “disposable PC,” something I would not normally
recommend that anybody purchase.
Most people were not aware of the semiproprietary nature of the design of these boards,
and they were extremely popular in what I call “retail store” PCs from the late 1980s
through the late 1990s. This would include primarily Compaq and Packard Bell systems,
aswellasmanyotherswhousedthisformfactorintheirlower-costsystems.Theseboards
were most often used in low-profile or Slimline case systems, but they were found in
towercases,too.Thesewereoftenlower-costsystemssuchasthosesoldatretailelectron-
ics superstores. LPX is considered obsolete today.
LPX boards are characterized by several distinctive features (see
Figure 4.5
). The most
noticeable is that the expansion slots are mounted on a bus riser card that plugs into the
motherboard. In most designs, expansion cards plug sideways into the riser card. This
sideways placement allows for the low-profile case design. Slots are located on one or
both sides of the riser card depending on the system and case design. Vendors who use
LPX-typemotherboardsintowercasessometimesuseaT-shapedrisercardinstead,which
puts the expansion slots at the normal right angle to the motherboard but on a raised shelf
above the motherboard.
Figure 4.5
Typical LPX system chassis and motherboard.
