MASSBUS was DEC's high-speed peripheral bus used primarily on larger PDP-10, PDP-11, and early VAX systems. It connected large disk and tape subsystems such as the RM and TU series directly to the CPU via dedicated MASSBUS adaptors. MASSBUS devices were physically enormous, power-hungry, and designed for machine-room environments, but provided excellent throughput for the era. It became strongly associated with "classic big iron" DEC systems.