| Designer | IBM |
|---|---|
| Bits | 64-bit |
| Introduced | 2000 |
| Version | ARCHLVL 2 and ARCHLVL 3 (2008) |
| Design | CISC |
| Type | Register-Memory Memory-Memory |
| Encoding | Variable (2, 4 or 6 bytes long) |
| Branching | Condition code |
| Endianness | Big |
| Registers | |
| General purpose | 16 |
| Floating point | 16 64-bit |
| IBM mainframe | Architecture |
| 700/7000 series | varied |
| System/360 | unified |
| System/370 | System/370 |
| S/370-XA | |
| ESA/370 | |
| System/390 | ESA/390 (ARCHLVL 1) |
| zSeries | z/Architecture 1 (ARCHLVL 2) |
| System z9 | |
| System z10 | z/Architecture 2 (ARCHLVL 3) |
| zEnterprise z196 | |
| zEnterprise z114 | |
z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), refers to IBM's 64-bit computing architecture for IBM mainframe computers. IBM introduced its first z/Architecture-based system, the zSeries Model 900, in late 2000. Later z/Architecture systems include the IBM z800, z990, z890, System z9 and the System z10. 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.
Most operating systems, including z/OS, restrict code execution to the first 2 GB (31 bits) of each virtual address space for reasons of efficiency and compatibility rather than architectural limits. The z/OS's virtual memory implementation supports multiple 2 GB address spaces, permitting more than 2 GB of concurrently resident program code. The 64-bit version of Linux on System z allows code to execute from 64-bit address ranges.
The z/VSE Version 4, z/TPF Version 1 and z/VM Version 5 operating systems, and presumably their successors, require z/Architecture.
z/Architecture supports running multiple concurrent operating systems and applications even if they use different addressing modes. This allows software developers to choose the addressing mode that is most advantageous for their applications and data structures.
Platform Solutions Inc. (PSI) previously marketed Itanium-based servers which were compatible with z/Architecture. IBM bought PSI in July, 2008, and the PSI systems are no longer available.[1] FLEX-ES and the Hercules emulator also implement z/Architecture. Hitachi mainframes running newer releases of the VOS3 operating system implement ESA/390 plus Hitachi-unique CPU instructions, including a few 64-bit instructions. While Hitachi was likely inspired by z/Architecture (and formally collaborated with IBM on the z800 model, introduced in 2002), Hitachi's machines are not z/Architecture-compatible.
IBM recognizes two z/Architecture ALS ("Architecture Level Sets"), known as ARCHLVL 2 and ARCHLVL 3, which define IBM's operating system support. IBM's practice is that IBM software products will specify a particular minimum ALS requirement. Software products are then compatible with machines that implement the minimum or higher ALS. Software can utilize new or enhanced CPU instructions found in models not defined in the ALS, but the software must not require instructions outside the ALS. IBM declares a new ALS when new software must require new or enhanced CPU instructions. IBM's z900, z800, z990, z890, System z9 EC, and System z9 BC machines implement ARCHLVL 2. The System z10 EC and System z10 BC machines implement ARCHLVL 3. IBM declared this new ALS on July 7, 2009,[2] when IBM also disclosed that z/VM Version 6.1 would require the new ALS.
OpenSolaris for System z runs on all ARCHLVL 3 machines and is also compatible with the last ARCHLVL 2 machine, the System z9.