Hardware Reference
In-Depth Information
AT systems use the smaller 6-pin mini-DIN connector (sometimes called a PS/2-type connector ) and
might even have a mouse connector. All other connectors are mounted on the case or on card edge
brackets and are attached to the motherboard via cables. The keyboard connector is visible through an
appropriately placed hole in the case.
See the Chapter 15 section, “ Keyboard/Mouse Interface Connectors ,” p. 751 .
All Baby-AT boards conform to specific widths and screw hole, slot, and keyboard connector
locations, but one thing that can vary is the length of the board. Versions have been built that are
smaller than the full 9 inches × 13 inches; these are often called mini-AT , micro-AT , or even things
such as 2/3-Baby or 1/2-Baby . Even though they might not be the full size, they still bolt directly into
the same case as a standard Baby-AT board and can be used as a direct replacement for one.
LPX
The LPX and mini-LPX form factor boards were a semiproprietary design that Western Digital
originally developed in 1987 for some of its motherboards. The LP in LPX stands for Low Profile,
which is so named because these boards incorporate slots that are parallel 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 mounted 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, as well as many others who used
this form factor in their lower-cost systems. These boards were most often used in low-profile or
Slimline case systems, but they were found in tower cases, too. These were often lower-cost systems
such as those sold at retail electronics 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-type motherboards in tower cases sometimes use a T-
shaped riser card instead, which puts the expansion slots at the normal right angle to the motherboard
but on a raised shelf above the motherboard.
 
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