ESA/390
(Redirected from 31-bit)
Categories: Computer architecture
| N-bit Processors | ||||||||
|---|---|---|---|---|---|---|---|---|
| 4-bit | 8-bit | 16-bit | 24-bit | 31-bit | 32-bit | 48-bit | 64-bit | 128-bit |
| N-bit Applications | ||||||||
| 16-bit | 31-bit | 32-bit | 64-bit | |||||
| N-bit Data Sizes | ||||||||
| 4-bit | 8-bit | 16-bit | 32-bit | 64-bit | 128-bit | |||
| nibble byte octet word dword qword | ||||||||
| These definitions are relevant to the world of x86 processors. See linked articles for discussion of the meaning in other architectures. The 31-bit and 48-bit sizes relate to IBM mainframes and AS/400s, respectively. | ||||||||
In computer architecture, 31-bit is an adjective used to describe integers, memory addresses or other data units that are at most 31 bits (just shy of 4 octets) wide, or to describe CPU and ALU architectures based on registers, address buses, or data buses of that size.
ESA/390 (Enterprise Systems Architecture/390) is IBM's most recent 31-bit mainframe computing design, copied by Amdahl, Hitachi, and Fujitsu among other competitors. z/Architecture, a 64-bit design, superseded ESA/390 in 2000.
ESA/390 is the only mainframe architecture implemented first with bipolar then later with CMOS electronics. The architecture maintained backward compatibility with the 24-bit System/360 (1964) and all intermediate large system 24/31-bit architectures (System/370, 370-XA, and ESA/370). ESA/390 is arguably a 32-bit architecture. Only memory addressing is limited to 31 bits. (IBM held one addressing bit in reserve to more easily support 24-bit applications.) In fact, system memory addressing is not limited to 31 bits, unlike most 31/32-bit architectures. A single address space cannot exceed 2 GB, but ESA/390 supports large numbers of address spaces, each up to 2 GB in size.
References
- ESA/390 Principles of Operation, IBM Publication No. SA22-7201.