LPX (Low Profile eXtension) form factor was a loosely defined mo"therboard 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 A TX 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 standardized specification, riser cards were seldom compatible from one motherboard design to another, much less one manufacturer to another.

The LPX format is a specialized variant of the Baby-AT used in low profile desktop systems and is a loose specification with a variety of proprietary implementations. Expansion slots are located on a central riser card, allowing cards to be mounteJ horizontally. However, this arrangement can make it difficult to remove the motherboard, and the more complex engineering required adds to system costs. As the riser card prevents good airflow within the system case, additional chassis fans are almost alway' needed.



The specification was very popular in the early. mid 90's, and briefly displaced the AT form factorai the most commonly used. However, the release Ii 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 AGr format was another blow, as the design not onh increased the pin count 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 IVai phased out around 1998. NLX was the intended successor, though many manufacturers chose Micro A TX or proprietary motherboard formats instead.