LPX (form factor)

LPX (short for Low Profile eXtension), originally developed by Western Digital, was a loosely defined motherboard format (form factor) widely used from 1987 to the late 1990s.

[1][2] There was never any official LPX specification, but the design normally featured a 13 × 9 in (330 × 229 mm) motherboard with the main I/O ports mounted on the back (something that was later adopted by the ATX form factor), and a riser card in the center of the motherboard, on which the PCI and ISA slots were mounted.

This layout was first used on IBM's PS/2 Model 30 personal computer, which Western Digital used as the basis for the creation of LPX.

[2] Due to the lack of standardized specification, riser cards were seldom compatible from one motherboard design to another, much less one manufacturer to another.

One of the more successful features to come out of the LPX specification was its use of more compact power supplies, which later became widely used on Baby AT and even full size AT cases.