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Concept
MVS
Summary
Multiple Virtual Storage, more commonly called MVS, is the most commonly used operating system on the System/370, System/390 and IBM Z IBM mainframe computers. IBM developed MVS, along with OS/VS1 and SVS, as a successor to OS/360. It is unrelated to IBM's other mainframe operating system lines, e.g., VSE, VM, TPF.
First released in 1974, MVS was extended by program products with new names multiple times, retaining the term MVS in the nomenclature:
first to MVS/SE (MVS/System Extensions),
next to MVS/SP (MVS/System Product) Version 1,
next to MVS/XA (MVS/eXtended Architecture),
next to MVS/ESA (MVS/Enterprise Systems Architecture),
and then extended
to OS/390 for the System/390 systems, and
finally to z/OS (when 64-bit support was added with the zSeries models). IBM added UNIX support (originally called OpenEdition MVS) in MVS/SP V4.3 and has obtained POSIX and UNIXTM certifications at several different levels from IEEE, X/Open and The Open Group. The MVS core remains fundamentally the same operating system. By design, programs written for MVS run on z/OS without modification.
At first IBM described MVS as simply a new release of OS/VS2, but it is, in fact a major rewrite. OS/VS2 release 1 is an upgrade of OS/360 MVT that retained most of the original code and, like MVT, is mainly written in assembly language. The MVS core is almost entirely written in Assembler XF, although a few modules were written in PL/S, but not the performance-sensitive ones, in particular not the Input/Output Supervisor (IOS). IBM's use of "OS/VS2" emphasized upwards compatibility: application programs that ran under MVT did not even need recompiling to run under MVS. The same Job Control Language files could be used unchanged; utilities and other non-core facilities like TSO ran unchanged. IBM and users almost unanimously called the new system MVS from the start, and IBM continued to use the term MVS in the naming of later major versions such as MVS/XA.
Official source
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