Z/Architecture

z/Architecture
DesignerIBM
Bits64-bit
Introduced2000; 24 years ago (2000)
VersionARCHLVL 2 and ARCHLVL 3 (2008)
DesignCISC
TypeRegister–Register
Register–Memory
Memory–Memory
EncodingVariable (2, 4 or 6 bytes long)
BranchingCondition code, indexing, counting
EndiannessBig
PredecessorESA/390
Registers
Access 16× 32, breaking-event-address register (BEAR) 64-bit, Control 16×64, Floating Point Control 32-bit, Prefix 64 bit, PSW 128-bit
General-purpose16× 64-bit
Floating point16× 64-bit
Vector32× 128-bit, VR0-VR15 contain FPR0-FPR15

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.[1] 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.

z/Architecture retains backward compatibility with previous 32-bit-data/31-bit-addressing architecture ESA/390 and its predecessors 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.[2] 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.

  1. ^ Development and Attributes of z/Architecture Archived 2013-12-12 at the Wayback Machine, IBM Journal of Research and Development, 2002.
  2. ^ "Accommodate functions for the z13 server to be discontinued on future servers". IBM. 25 June 2015. Archived from the original on 2017-09-15. Retrieved 2017-09-18.