A riser board is a circuit board that gives a computer motherboard the option for additional expansion cards to be added to the computer. Desktop computer riser boards were used with LPX, NLX, and even some ATX motherboards. LPX motherboards had a riser board slot on the motherboard, NLX motherboards plugged into the riser board, and Intel did introduce a version of an ATX motherboard in December of 1999 that supported either two or three PCI cards, but never supported AGP.
Today, riser boards are rarely used or found in desktop computers, which mostly use an ATX motherboard with expansion slots on the motherboard. However, there are still many servers and routers that use riser boards. Below, is a picture of a 4-slot riser board used with an early Compaq computers that plugs into the motherboard and gives the computer the ability to add four additional expansion cards.