LPX
Motherboard form factor originally developed by Western Digital when it was making motherboards that was used in the 1990s. The LPX motherboard is 9" wide x 13" deep, uses a riser card, and has different placement of the video, parallel, serial, and PS/2 ports on the back. Below is a picture example of what an LPX motherboard may have looked like. This is a picture of a Packard Bell LPX motherboard and as can be seen has one large brown slot that the riser card would connect into.
Also see: Form factor, Motherboard definitions, P8 / P9 connector