(^76) PC Hardware: A Beginner’s Guide
Micro-AT Form Factor
Further high-scale integration of processor chipsets and supporting components lead to
the development of a motherboard size even smaller than the Baby AT. The Micro-AT
motherboard, which fit in both the AT and Baby AT system cases, was nearly half the size
of the Baby AT main board.LPX and Mini-LPX Specifications
The LPX and Mini-LPX motherboard specifications are not actually form factors because
they lack a specific motherboard standard; they are more of a general motherboard design.
Originally developed by Western Digital as a part of their effort to slim down computer
cases,theLPXandMini-LPXhavebeencopiedbymanyothercompanies,eachgivingthe
designtheirownvariationoftheoriginalspecification.PackardBellandCompaq,among
other computer manufacturers, have used their own proprietary configurations of the
LPX or Mini-LPX motherboards in their PCs. Because there is no industry-wide standard
for this board, the users who purchase these systems could not upgrade their PCs with-
out changing out the motherboard.
A daughterboard (riser board) that plugs into a mounting slot that runs down the
middleofthemotherboardcharacterizestheLPX-stylemotherboard.Thedaughterboard
contains two or three peripheral expansion slots, depending on the size of the daughter-
board and whether it has slots on both sides. Because the expansion cards are mounted
sideways on the daughterboard, less space is required and the case size is smaller.
The LPX-style also integrates device controllers on the motherboard, including
controllers for IDE (Integrated Drive Electronics), video, and sound devices. This also
helps to reduce the case size by reducing the number of expansion slots required on the
daughterboard.
The external connections on the LPX-style boards are mounted in a row (see Figure 4-2).
This allows for easy access to keyboard and mouse connectors, serial ports, parallel ports,
and video and audio connectors. Some LPX versions also include USB (Universal Serial
Bus) connectors or an onboard NIC (network interface card).
In spite of the fact that many of the LPX motherboard’s design features were very
innovative, the lack of a standard form factor that would allow for easy upgrade made it
unattractive to users. However, the best innovations of the LPX were incorporated into
the next-generation form factors, the ATX and NLX boards, which are discussed in the
following sections.ATX Form Factor
The ATX form factor, released by Intel in 1995, was an improvement over the LPX form
factor because it is a published and continuously maintained specification for mother-
boards, cases, and power supplies. All ATX cases and boards are guaranteed compatibility
among all adopters of the standard.
The ATX form factor is generally based on the smaller Baby AT motherboard size.
However, size is about the only thing they have in common. ATX is a completely new design