z/Architecture, initially called ESA Modal Extensions (ESAME), refers to
IBM's 64-bitcomputing architecture for a current generation of its mainframe computers. IBM introduced its first z/Architecture-based system, the zSeriesModel 900, in late 2000. Later z/Architecture systems included the IBM z800, z990, z890, System z9and the System z10. z/Architecture retains backward compatibilitywith previous 31-bit architecture ESA/390and its predecessors all the way back to the 24-bit System/360.
operating systems running on z/Architecture systems vary in how much they exploit the 64-bit design. Currently most operating systems, including z/OS, continue to restrict code execution to the first 2 GB (31 bits) of each virtual address space solely for reasons of efficiency and compatibility, allowing only data objects to reach into the higher 64-bit addressing ranges. Since z/OS virtual memoryimplementation supports multiple 2 GB address spaces, this restriction still allows to utilize much more than 2 GB of resident code concurrently. The 64-bit version of Linux on System zallows code to execute from 64-bit address range.
Among the other major operating systems,
z/VSEVersion 4, z/TPFVersion 1, and z/VMVersion 5, and presumably their successors, all require z/Architecture.
z/Architecture supports running multiple concurrent operating systems and applications even if they use different "addressing modes". Thus developers can choose whichever addressing modes are most advantageous for their applications and data structures.
Platform Solutions, Inc., marketed
Itanium-based servers that could run System z applications and operating systems. PSI was bought by IBM in July 2008. [cite press release| title=IBM Acquires Platform Solutions |publisher=IBM |date=2008-07-02 |url=http://www-03.ibm.com/press/us/en/pressrelease/24560.wss |accessdate=2008-09-06] The z/Architecture is also emulated by the Hercules emulator.
* [http://www.research.ibm.com/journal/rd/464/plambeck.html Development and Attributes of z/Architecture] , IBM Journal of Research and Development, 2002.
* [http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/XKS/DZ9ZBK07 z/Architecture Principles of Operation and Reference Summary]
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