MVT

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MVT is an acronym for Multiprogramming with a Variable number of Tasks. It was the most sophisticated variant of the OS/360 operating system for the IBM System/360 line of computers. It was intended as the operating system for the larger machines in the System/360 family, introduced in 1964, but MVT did not become available until 1967. Early versions had many problems and the simpler MFT continued in use for many years. It is a very old forerunner of IBM's MVS and z/OS.

Long since dead and buried, it is of historical interest as the most advanced of the early OS/360 operating systems and the one most influential in later developments.

In particular, the I/O queueing of all the OS/360 family left a lot to be desired. This was addressed by two field-developed packages: HASP (Houston Automated Spooling Package), and ASP. ASP stood for Attached Support Processor, which was something like a 360/40 controlling a 360/65 or greater processor through a magnetic tape channel controller processor. In effect, ASP required the purchase of a second computer. In contrast, HASP needed only one computer, such as a 360/65 alone, and MFT to start with. Later, with MVS, HASP was the standard.

HASP was developed by IBM Federal Systems Division contractors at the Johnson Space Center in Houston. In MVS, HASP became JES2, one of two versions of the Job Entry Subsystem. It was many years before the HASP labels were removed from the JES2 source, and the messages issued by JES2 are still prefixed with $HASP.

ASP was developed to provide efficient use of multiple OS/360 systems working in conjunction, and allowed one central system to distribute jobs to multiple connected systems. ASP became JES3.