Backplanes are boards with a series of connectors attached to them in parallel. They are often located on the rear of a card rack allowing connection for other boards or devices to be inserted into the connectors. The number of channels range from 2 to 21 with interface options such as CompactPCI, Standard Bus, Uncommitted, VME J1, VME J1/J2, and VME J1/J2/J0.