z/Architecture
z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architecture-based system, the z900, in late 2000. Later z/Architecture systems include the IBM z800, z990, z890, System z9, System z10, zEnterprise 196, zEnterprise 114, zEC12, zBC12, z13, z14, z15 and z16.
| Designer | IBM |
|---|---|
| Bits | 64-bit |
| Introduced | 2000 |
| Version | ARCHLVL 2 and ARCHLVL 3 (2008) |
| Design | CISC |
| Type | Register–Register Register–Memory Memory–Memory |
| Encoding | Variable (2, 4 or 6 bytes long) |
| Branching | Condition code, indexing, counting |
| Endianness | Big |
| Predecessor | ESA/390 |
| Registers | |
| General-purpose | 16× 64-bit |
| Floating point | 16× 64-bit |
| Vector | 32× 128-bit |
| History of IBM mainframes, 1952–present |
|---|
| Market name |
| Architecture |
z/Architecture retains backward compatibility with previous 32-bit-data/31-bit-addressing architecture ESA/390 and its predecessors all the way back to the 32-bit-data/24-bit-addressing System/360. The IBM z13 is the last z Systems server to support running an operating system in ESA/390 architecture mode. However, all 24-bit and 31-bit problem-state application programs originally written to run on the ESA/390 architecture will be unaffected by this change.