OS/VS1

History of IBM mainframe operating systems
Early mainframe computer OSs GM OS & GM-NAA I/O (1955) BESYS (1957) UMES (1958) SOS (1959) IBSYS (1960) CTSS (1961)
Miscellaneous S/360 line OSes 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)

Operating System/Virtual Storage 1, or OS/VS1, was an IBM mainframe computer operating system designed to be run on IBM System/370 hardware. It was the successor to the Multiprogramming with a Fixed number of Tasks (MFT) option of System/360's operating system OS/360. OS/VS1, in comparison to its predecessor, supported virtual memory (then called virtual storage).^[1] OS/VS1 was generally available during the 1970s and 1980s, and it is no longer supported by IBM.

OS/VS1 was OS/360 MFT II with a single virtual address space; by comparison, OS/VS2 SVS was OS/360 MVT with a single virtual address space. OS/VS1 was often installed on mid-range IBM mainframe systems, such as the System/370 Model 148.^[2]

OS/VS1 was intended to manage a medium-sized work load (for the 1970s) consisting only of batch processing applications, running within a fixed number of operating system partitions via the batch job management system Job Entry Subsystem 1 (JES1). This was in contrast to OS/VS2 which was intended to handle larger work loads consisting of batch applications, online interactive users (using the Time Sharing Option, or TSO), or a combination of both. However, OS/VS1 could, and often did, support interactive applications and users by running IBM's CICS transaction processing monitor as a job within one of its partitions.^[3]

Installation and modification of OS/VS1 was accomplished via IBM's cumbersome System Generation (SYSGEN) process.

OS/VS1 went through seven product releases. OS/VS1 Release 7 was enhanced by fourth release of the IBM OS/VS1 Basic Programming Extensions (BPE) product. BPE provided support for new 1980s hardware, such as 3380 DASD (disk).

The last OS/VS1 product release, OS/VS1 Basic Programming Extensions (BPE) Release 4, was announced by IBM in 1983 for general availability in March 1984 (product 5662-257, announcement letter 283-266, 15 September 1983).

IBM announced the end of functional enhancements to OS/VS1 in 1984.^[4] IBM recommended OS/VS1 installations migrate to MVS/370 or MVS/XA. To assist with the migration to MVS/XA, IBM made the VM/XA Migration Aid. It allowed installations to run OS/VS1 and MVS/XA simultaneously on the same machine, as guests of a third system - VM/XA. This way, the new MVS/XA system could be tested while the old production OS/VS1 system was still in use.

References

↑ IBM press release concerning memory virtualization from 2005
↑ "System/370 Model 148", IBM
↑ "History of CICS", IBM
↑ OS/VS1 Consolidated Stabilization Statement, product 5652-VS1, announcement letter 284-086, 23 February 1984.

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