Editing History of operating systems (section)

===Systems on IBM hardware===
{{main|History of IBM mainframe operating systems}}

The state of affairs continued until the 1960s when [[IBM]], already a leading hardware vendor, stopped work on existing systems and put all its effort into developing the [[IBM System/360|System/360]] series of machines, all of which used the ''same'' instruction and input/output architecture. IBM intended to develop a single operating system for the new hardware, the [[OS/360 and successors|OS/360]]. The problems encountered in the development of the OS/360 are legendary, and are described by [[Fred Brooks]] in ''[[The Mythical Man-Month]]''—a book that has become a classic of [[software engineering]]. Because of performance differences across the hardware range and delays with software development, a whole family of operating systems was introduced instead of a single OS/360.<ref name="JohnsonVSEPast40Years">{{cite journal
 | last        = Johnston
 | date        = April 1, 2005
 | title       = VSE: A Look at the Past 40 Years
 | journal     = z/Journal
 | issue       = April/May 2005
 | publisher   = Thomas Communications, Inc.
 | url         = http://www.zjournal.com/index.cfm?section=article&aid=293
 | url-status  = dead
 | archive-url  = https://web.archive.org/web/20090304014628/http://www.zjournal.com/index.cfm?section=article&aid=293
 | archive-date = March 4, 2009}}</ref><ref name="Boyer360Revolution">{{cite web |author=Chuck Boyer |url=https://www.vm.ibm.com/history/360rev.pdf |title=The 360 Revolution}}</ref>

IBM wound up releasing a series of stop-gaps followed by two longer-lived operating systems:
* [[OS/360 and successors|OS/360]] for mid-range and large systems. This was available in three [[System Generation (OS)|system generation]] options:
** [[OS/360 and successors#PCP|PCP]] for early users and for those without the resources for multiprogramming.
** [[OS/360 and successors#MFT|MFT]] for mid-range systems, replaced by MFT-II in OS/360 Release 15/16. This had one successor, [[OS/VS1]], which was discontinued in the 1980s.
** [[OS/360 and successors#MVT|MVT]] for large systems. This was similar in most ways to PCP and MFT (most programs could be ported among the three without being [[compiler|re-compiled]]), but has more sophisticated memory management and a [[time-sharing]] facility, [[Time Sharing Option|TSO]]. MVT had several successors including the current [[z/OS]].
* [[DOS/360 and successors|DOS/360]] for small System/360 models had several successors including the current [[VSE (operating system)|z/VSE]]. It was significantly different from OS/360.

IBM maintained full compatibility with the past, so that programs developed in the sixties can still run under z/VSE (if developed for DOS/360) or z/OS (if developed for MFT or MVT) with no change.

IBM also developed [[TSS (operating system)|TSS/360]], a time-sharing system for the [[IBM System/360 Model 67|System/360 Model 67]]. Overcompensating for their perceived importance of developing a timeshare system, they set hundreds of developers to work on the project. Early releases of TSS were slow and unreliable; by the time TSS had acceptable performance and reliability, IBM wanted its TSS users to migrate to OS/360 and OS/VS2; while IBM offered a TSS/370 PRPQ, they dropped it after 3 releases.<ref>{{cite web |url=http://www.beagle-ears.com/lars/engineer/comphist/ibm360.htm |title=IBM 360/370/3090/390 |author=Lars Poulsen |date=26 October 2001 |work=Computer History |access-date=18 November 2015}}</ref>

Several operating systems for the IBM S/360 and S/370 architectures were developed by third parties, including the [[Michigan Terminal System]] (MTS) and [[MUSIC/SP]].