OS/360
OS/360 was a
batch processing operating system developed by
IBM for their then-new
System/360 mainframe computer, announced in
1964. OS/360 was amongst the earliest operating systems to make direct access storage devices a prerequisite for its operation.
Main structure
OS/360 was developed as a family of three control programs, which increased in size as well as functionality. Initially, the single task PCP (Primary Control Program) processed jobs sequentially; the next, MFT (Multiprogramming with a Fixed number of Tasks) added multitasking, but only allowed a fixed number of concurrent tasks, each one having a preset memory allocation. Finally MVT (Multiprogramming with a Variable number of Tasks) allowed varying numbers of tasks whose memory size could change dynamically. OS/360 also introduced IBM's batch-scripting language JCL (Job Control Language).
History
OS/360 was late being delivered, due to a combination of organizational disarray inside IBM and lack of experience with the pitfalls of large software projects, as well as the significant technical challenges. Originally scheduled for delivery in 1965 (for the simplest versions) and 1966 (for the more complex ones), it ended up being a year late — it was not released in its first production versions until 1966 and 67 (PCP and MVT, respectively).
A family of simple alternative systems, BOS (Basic Operating System, for the smallest machines), TOS (Tape Operating System, for machines with only tape drives), and DOS (Disk Operating System), was hurriedly put together to allow customers to use the new machines. Although intended as a temporary interim tool, DOS survived until 1971.
When virtual addressing hardware was later developed for the System/370, the systems were upgraded and renamed; MFT became OS/VS1 and MVT became OS/VS2. OS/VS2 was announced in two forms: OS/VS2 Release 1, aka SVS (Single Virtual Storage) and OS/VS2 Release 2, aka MVS (Multiple Virtual Storage). SVS was intended as a stepping stone from MVT to MVS, and is only of historical interest today. MVS is still used on the latest members of the IBM 360 Series. As of the turn of the millennium, the original OS/360 is in the public domain and can be downloaded freely. As well as being run on actual System/360 hardware, it can execute on the free Hercules emulator which runs under GNU/Linux and Windows.
After his experience running the System/360 project, and later specifically in charge of the (by then long overdue) OS/360, Frederick P. Brooks wrote his famous book, The Mythical Man-Month, citing OS/360 as a very realistic and comprehensive example of the second-system effect.
References
\n* Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and Early 370 Systems. MIT Press, Cambridge, MA. (pp. 291-345)
External links
\n* MVS... a long history: OS/360\n* Operating System/360 1965-1972
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This article (or an earlier version of it) contains material from FOLDOC's article on OS/360, used with permission.
Category:IBM software\nCategory:Operating systems
