The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts.

The Unibus was developed around 1969 by Gordon Bell and student Harold McFarland while at Carnegie Mellon University.

Unifying these formerly separate busses allowed external devices to easily perform direct memory access (DMA) and made the construction of device drivers easier as control and data exchange was all handled through memory-mapped I/O.

[2] Unibus was physically large, which led to the introduction of Q-bus, which multiplexed some signals to reduce pin count.

The Unibus consists of 72 signals, usually connected via two 36-way edge connectors on each printed circuit board.