LPX (form factor)

LPX (short for low profile extension) was a loosely defined motherboard format (form factor) widely used from the late 1980s to the late 1990s. The format was originally developed by Western Digital who based their design off the IBM PS/2 Model 30. A defining feature of motherboards with the LPX form factor is the integration of controllers and ports, which used to be separate add-ons on the earlier AT and Baby AT motherboards, as well as riser cards and slimline power supplies. The use of a riser card to horizontally position expansion cards allowed computer cases designed around LPX motherboards to be much smaller than earlier AT-based cases.

Overview

There was never any official LPX specification, but the design usually featured a 13 × 9 in (330 × 229 mm) motherboard with the main I/O ports mounted along the back edge (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. Western Digital's reference design was released as the WD30-WDM, unveiled in late 1987 and sold starting in spring 1988. A clone of the PS/2 Model 30's motherboard, it contains integrated parallel and serial controllers and ports, floppy and hard disk controllers, a VGA controller, and a three-slot 8-bit ISA riser card.

Due to the lack of standardized specification, riser cards were rarely compatible from one motherboard design to another, much less one manufacturer to another. The internal PSU connector was of the same type used in the AT form factor.

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