When IBM announced the System/360 mainframe line in April 1964, the plan was to provide just one operating system for batch-oriented use, known simply as the System/360 Operating System (less formally as OS/360, or OS). OS was big, complex and ambitious for its day, and the resulting system was late, buggy and resource-intensive. Installations that couldn't wait, or couldn't afford the hardware required to run OS, opted for one of the smaller, simpler systems that IBM created as alternatives: BOS/360, TOS/360, DOS/360. Eventually, with most of the bugs shaken out OS/360 became IBM's flagship System/360 operating system.
By the time of the final OS/360 release in 1974, system programmers building an OS system had the choice of two control programs: MFT, Multiprogramming with a Fixed number of partition Tasks, and MVT, Multiprogramming with a Variable number of region Tasks. (A third control program option, PCP, Primary Control Program, had been discontinued. PCP could only run one job at a time, which wasted expensive mainframe hardware resouces. Any machine not big enough to run MFT or MVT generally ran DOS/360 instead.)
MVT offered more flexibility and power than MFT, but the price of MVT's advantages was a higher main storage requirement. Because main storage was probably the single most expensive component of System/360 hardware, adding storage was not trivial, and smaller OS shops made do with MFT.
While MVT provided more capabilities than other System/360 operating system alternatives, it was not complete, and add-on products were developed to fill in the gaps. Many users replaced the primitive spool functionality provided natively by MVT with HASP. A few very large installations used ASP to provide not only spooling but loosely coupled multiprocessing and workload management.
Release 21.8, the final version of OS/360, survives on the Web in several places. Virtual tapes containing the vanilla IBM 2311 OS/360 distribution are available from the IBM Public Domain Software Collection at ibiblio.org. Also at ibiblio.org is a turnkey MVT 21.8 system that I built with ASP and HASP preinstalled.
Some OS/360 publications at bitsavers.org that you might find useful:
- GC28-6554-13 OS Release 21.8 System Generation
- GC28-6631-13 OS/360 Release 21.7 Messages and Codes
- GC28-6720-4 OS/360 Release 21 MVT Guide
- GC28-6691-3 OS/360 Release 21 Operator Reference
- GC28-6670-6 OS/360 Release 21 Programmer's Guide to Debugging
- GC28-6628-9 OS/360 Release 21.7 System Control Blocks
No system is complete without programs to run on it, and local modifications to make it run as the user desires. Below you will find links to:
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