IBM Single Virtual Storage (SVS)
| Developer | IBM |
|---|---|
| OS family | OS/360 |
| Latest release | Release 1.7 |
| Platforms | S/370 |
| License | none |
| Preceded by | OS/360 |
| Succeeded by | OS/VS2 (MVS) |
Single Virtual Storage (SVS) refers to Release 1 of Operating System/Virtual Storage 2 (OS/VS2); it is the successor system to the MVT option of Operating System/360. OS/VS2 (SVS) was a stopgap measure pending the availability of MVS, although IBM provided support and enhancements to SVS long after shipping MVS.
SVS provides a single 16MiB address space which is shared by all tasks in the system, regardless of the size of physical memory.
OS/360 used the Interval Timer feature for providing time of day and for triggering time-dependent events. The support for S/370 made limited use of new timing facilities, but retained a dependency on the Interval Timer. SVS uses the TOD Clock, Clock Comparator and CPU Timer exclusively.
In the wake of the Applied Data Research lawsuit IBM decided to develop chargeable versions of several applications, mostly language processors, although it's not clear whether the lawsuit was actually the deciding factor. As a result, SVS does not include a sort/merge program or any language processor other than the new Assembler (XF), which is required for the system generation process.
Authorized Program Facility (APF) is a new facility that limited use of certain dangerous services to programs that are authorized, that is link edited with AC(1) and were loaded from the link list, LPA, or SYS1.SVCLIB. In MVS IBM enhanced the facility to allow the installation to designate additional data sets as authorized.
Because the Reader/Interpreter in SVS runs in pageable storage, there is much less benefit to the Automatic SYSIN Batching (ASB) Reader, and SVS does not include it. OS/360 had a facility called Direct SYSOUT (DSO) whereby specific output classes could be diverted to data sets on tape instead of normal SPOOL datasets. As DASD prices dropped, the facility dropped from use, and SVS did not provide it.
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