LPX (form factor)

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LPX (Low Profile eXtension) was a loosely defined motherboard format (form factor) widely used in the 1990s.

There was never any official LPX specification, but the design normally used consisted of the main I/O ports mounted on the back of the motherboard (something 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. The PSU was of the same type used in the AT form factor. Due to the lack of standardised specification, riser cards were seldom compatible from one motherboard design to another, much less one manufacturer to another.

The specification was very popular in the early-mid 90's, and briefly displaced the AT form factor as the most commonly used. However, the release of the Pentium II in 1997 effectively consigned the format to death, as a good airflow was important in Pentium II systems, and LPX systems normally had a rather poor airflow. The introduction of the AGP format was another blow, as the design not only increased the pincount on riser cards, but it limited most cards to one AGP, one PCI and one ISA slot, which was too restrictive for most users.

LPX was phased out around 1998. NLX was the intended successor, though many manufacturers chose MicroATX or proprietary motherboard formats instead.