Operating System/Virtual Storage 1, or OS/VS1, is a discontinued 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.

Working stateHistoric
Latest releaseOS/VS1 Basic Programming Extensions (BPE) Release 4 / March 1984 (1984-03)
Marketing targetIBM mainframes
History of IBM mainframe operating systems


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 145 and, later, 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.

Remote Entry Services (RES)

OS/VS1 included a replacement for OS/360 RJE. It allowed submission and retrieval of jobs by 2770, 2780 and 3780 terminals and by workstation programs included with OS/VS1 for, e.g., 1130. RES included Remote Terminal Access Method and a closer integration with Job Management than what RJE had.

IBM upgrades

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.


Although IBM's Time Sharing Option (TSO) required VS2, customers with a 370/145 or 370/148 had other time-sharing options.
One combination was VM/CMS for time sharing, and a guest "machine" running OS/360 MFT II for batch.[5]

Conversational Remote Job Entry

Optional component of OS/360 MFT II, OS/360 MVT and OS/VS1, CRJE allowed the user at a line-mode terminal to edit text datasets, submit jobs and access job output.

TONE for VS1

A non-IBM time-sharing product named TONE (TSO-like, for VS1 / VS ONE)[6] was marketed by Tone Software Co.[7]


  1. IBM press release concerning memory virtualization from 2005
  2. "System/370 Model 148", IBM
  3. "History of CICS", IBM
  4. OS/VS1 Consolidated Stabilization Statement, product 5652-VS1, announcement letter 284-086, 23 February 1984.
  5. During the 1970s, some universities ran the above combination during the day, and "went native" (no VM/CMS) at night, to run heavy batch work, e.g. administrative
  6. mentioned in Computerworld, Dec. 6, 1976, p. 22; the article mentions the planned 1977 release of version III of Tone)
  7. the p. 72 ad from the Feb. 21, 1977 issue of Computerworld, can be found at https://books.google.com/books?id=LD44Qbu9AsUC&pg=PA72&lpg=PA72 and the headline says "The ONLY COMPLETE TIME SHARING SYSTEM FOR VS1"

Further reading

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