Riser cards, sometimes called daughterboards depending on their usage, are found in motherboards that are designed for small form factor computers. Riser cards are used to add expansion slots to a board, but unlike on standard motherboards, the expansion cards install perpendicular to the board. Only a few form factors use riser cards.
LPX
Western Digital designed low profile extended (LPX) motherboards in 1987. Due to its small size, the motherboard was often used in slim-line desktop computers and was popular throughout the late 1980s and 1990s. LPX had one major drawback, however: the form factor wasn't standardized. Riser cards and other components designed for one LPX motherboard wouldn't work with another, and as a result, people who had purchased an LPX system could not upgrade or repair the computer. The LPX form factor includes one to two expansion slots. On motherboards designed for tower cases, the riser card ran perpendicular to the board but was installed on its own shelf.
NLX
New low profile extended (NLX) replaced LPX in the mid 1990s. Intel developed the NLX form factor to improve and standardize the LPX design. Like the LPX, NLX was used for slim-line computers, but rather than manufactured for consumers, the form factor was popular in the corporate market instead. Unlike the LPX and most other motherboard form factors, the riser was a central component; the motherboard and all internal cables plugged into the riser card. Upgrading and repairing motherboards on the NLX, as a result, was a much simpler task than it was with the LPX, as it required little more than disconnecting the riser from the old motherboard and plugging it into the new one.
PicoBTX
Intel released the balanced technology extended (BTX) form factor in 2003, intending to replace advanced technology extended, which at the time was perceived as dated. BTX improved on some of the issues that plagued the ATX -- such as poor heat dissipation -- but the form factor never picked up much steam. PicoBTX is an off-shoot of BTX; the form factor is designed for entertainment and mobile systems. Unlike BTX, the PicoBTX uses a riser card to enable the motherboard to fit in small cases.
Mini-ITX
VIA Technologies developed Mini-ITX in 2001. Mini-ITX, a mere 17 cm-by-17 cm, is found in wireless equipment, set-top boxes and home theater systems. The Mini-ITX traditionally includes one expansion slot that runs perpendicular to the motherboard, but on some models you can install a two-slot riser card to the existing expansion slot.
Tags: form factor, riser card, expansion slot, expansion slots, factors riser