OS/360 and Successors | OS 360 Successors

OS/360 And Successors

OS/360, officially known as IBM System/360 Operating System, was a batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was heavily influenced by the earlier IBSYS/IBJOB and Input/Output Control System (IOCS) packages. It was among the earliest operating systems to make direct access storage devices a prerequisite for their operation.

IBM announced three different levels of OS/360, generated from the same tapes and sharing most of their code. IBM eventually renamed these options and made some significant design changes:

Single Sequential Scheduler (SSS)
- Option 1
- Primary Control Program (PCP)
Multiple Sequential Schedulers (MSS)
- Option 2
- Multiprogramming with a Fixed number of Tasks (MFT)
- MFT 2
Multiple Priority Schedulers (MPS)
- Option 4
- VMS
- Multiprogramming with a Variable number of Tasks (MVT)
- Model 65 Multiprocessing (M65MP)

Users often coined nicknames, e.g., Big OS, OS/MFT, but none of these names had any official recognition by IBM.

The other major operating system for System/360 hardware was DOS/360.

History of IBM mainframe operating systems
Early mainframe computers GM OS & GM-NAA I/O (1955) BESYS (1957) UMES (1958) SOS (1959) IBSYS (1960) CTSS (1961)
S/360 and successors BOS/360 (1965) TOS/360 (1965) TSS/360 (1967) MTS (1967) ORVYL (1967) MUSIC (1972) MUSIC/SP (1985)
DOS/360 and successors (1966) DOS/VS (1972) DOS/VSE (1980s) VSE/SP late (1980s) VSE/ESA (1991) z/VSE (2005)
OS/360 and successors (1966) MFT (1966) MFT II (1968) OS/VS1 (1972) OS/VS1 BPE MVT (1967) 65MP OS/VS2R1 (SVS) (1972) MVS (OS/VS2R2 and later) (1974) MVS/SE (1978) MVS/SE 2 (1979) MVS/SP Version 1 (1980) MVS/XA (1983) MVS/ESA (1988) OS/390 (1995) z/OS (2000)
VM line CP-40/CMS (1967) CP-67/CMS (1967) VP/CSS (1968) VM/370 (1972) VM/BSE (BSEPP) VM/SE (SEPP) VM/SP (1980) VM/XA MA (1984) VM/XA SF (1985) VM/XA SP (1988) VM/ESA (1990) z/VM (2000)
TPF line ACP (1967) TPF (1979) z/TPF (2005)
UNIX and Unix-like UTS (1981) AIX/370 (1990) AIX/ESA (1991) MVS/ESA OpenEdition (1993) OS/390 UNIX System Services (1996) Linux (1999) z/OS UNIX System Services (2001) OpenSolaris (2008)

OS/360 is in the public domain and can be downloaded freely. As well as being run on actual System/360 hardware, it can be executed on the free Hercules emulator, which runs under most UNIX and Unix-like systems including GNU/Linux, Solaris, and Mac OS X, as well as Windows. There are OS/360 turnkey CD's that provide pregenerated OS/360 21.8 systems ready to run under Hercules.