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OS/360, officially known as IBM System/360 Operating System,〔 is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was heavily influenced by the earlier IBSYS/IBJOB and Input/Output Control System (IOCS) packages. It was among the earliest operating systems to make direct access storage devices a prerequisite for their operation. Although OS/360 itself was discontinued, successor operating systems including the virtual storage MVS and the 64 bit z/OS are still run and maintain application-level compatibility. IBM announced three different levels of OS/360, generated from the same tapes and sharing most of their code. IBM eventually renamed these options and made some significant design changes: * Single Sequential Scheduler (SSS) * * Option 1 * * Primary Control Program (PCP) * Multiple Sequential Schedulers (MSS) * * Option 2 * * Multiprogramming with a Fixed number of Tasks (MFT) * * MFT 2 * Multiple Priority Schedulers (MPS) * * Option 4 * * VMS〔VMS was unrelated to the VMS system for the DEC VAX.〕 * * Multiprogramming with a Variable number of Tasks (MVT) * * Model 65 Multiprocessing (M65MP) Users often coined nicknames, e.g., Big OS, OS/MFT, but none of these names had any official recognition by IBM. The other major operating system for System/360 hardware was DOS/360. OS/360 is in the public domain and can be downloaded freely. As well as being run on actual System/360 hardware, it can be executed on the free Hercules emulator, which runs under most UNIX and Unix-like systems including GNU/Linux, Solaris, and Mac OS X, as well as Windows. There are OS/360 turnkey CDs that provide pregenerated OS/360 21.8 systems ready to run under Hercules. ==Origin== IBM originally intended that System/360 should have only one batch-oriented〔IBM eventually provided interactive facilities for OS/360, e.g., CRJE, ITF, TSO.〕 operating system, OS/360.〔 It also intended to supply a separate timesharing operating system, TSS/360. There are at least two accounts of why IBM eventually decided to produce other, simpler batch-oriented operating systems: because it found that OS/360 would not fit into the limited memory available on the smaller System/360 models; or because it realized that the development of OS/360 would take much longer than expected. IBM introduced a series of stop-gaps to prevent System/360 hardware sales from collapsing—first BOS/360 (Basic Operating System, for the smallest machines with 8K byte memories), then TOS/360 (Tape Operating System, for machines with at least 16K byte memories and only tape drives), and finally DOS/360 (Disk Operating System), which became a mainstream operating system and is the ancestor of today's widely used z/VSE.〔〔Chuck Boyer, (''The 360 Revolution'' )〕 IBM released three variants of OS/360: PCP (Primary Control Program), a short-lived stop-gap which could run only one job at a time, in 1966; MFT (Multiprogramming with Fixed number of Tasks) for the mid-range machines, and MVT (Multiprogramming with Variable number of Tasks) for the top end.〔Introduction, op. cit., page 50〕 MFT and MVT were used until at least 1981,〔http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-2782.pdf〕 a good five years after their successors had been launched.〔(The midseventies SHARE survey ) by an IBM user group〕 It is unclear whether the division between MFT and MVT arose because MVT required too much processing power to be usable on mid-range machines or because IBM needed to release a multiprogramming version of OS (MFT) as soon as possible. Initially IBM maintained that MFT and MVT were simply "two configurations of the () control program", although later IBM described them as "separate versions of OS/360".〔〔 IBM originally wrote OS/360 in assembly language. Later on, IBM wrote some OS/360 code in a new language, Basic Systems Language (BSL), derived from PL/I. A large amount of the TSO code in Release 20 was written in BSL. TSS/360 was so late and unreliable that IBM canceled it, although IBM later supplied three releases of the TSS/370 PRPQ. By this time CP-67 was running well enough for IBM to offer it without warranty as a timesharing facility for a few large customers.〔(The IBM 360/67 and CP/CMS )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「OS/360 and successors」の詳細全文を読む スポンサード リンク
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