The System/370 is a model range of IBM mainframes introduced in the early 1970s as the successors to the System/360 family. New architectural features distinct from the 360 range include: standard dual-processor capability, full support for virtual memory, and 128-bit floating point arithmetic.

The original System/370 line underwent two major architectural improvements during its roughly 20-year lifetime, both primarily involving expansions in memory (central storage) address space to support larger workloads, and both preserving backward compatibility. In the 1980s IBM introduced the 370/XA architecture as the first step in the upgrade from 24-bit to 31-bit addressing (IBM reserved one bit to facilitate backward compatibility). In the 1990s IBM introduced 370/ESA architecture (later named 390/ESA), finishing the evolution to full 31-bit virtual addressing.

The System/390 line replaced the System/370s in the 1990s.

Notable machines in the 370 range include the IBM 3033 , the IBM 3090 mainframe/supercomputer with its optional vector facility (VF) extension, and the relatively inexpensive IBM 9370 (tailored for small-to-medium size businesses). Amdahl competed aggressively against IBM with its IBM-compatible mainframes.

See also

• zSeries