The PDP-11/70 was introduced in 1975 at the top of the 11 range. The machines architecture was in many respects similar to that of the 11/45, but the 11/70 had expanded memory capacity, a reorganized I/O structure and a high-speed cache memory.

The 11/70 was equipped with a KD11-B CPU which featured a 2KB cache memory and 22-bit addressing. The maximum memory capacity thus increased to 4MB (2MW) with the 18-bit UNIBUS being mapped on using a UNIBUS mapping unit. These changes combined to give the 11/70 around three times the throughput of an 11/45