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An IBM mainframe is an International Business Machines (IBM)-made mainframe computer, i.e., a traditionally "large" high-performance computer (in terms of price tag, physical size, transaction processing and I/O performance), although usually not as expensive and highly performing as a supercomputer.
Description In the early years (1950–1965) IBM made many models of mainframes, most of which were incompatible with each other. It had two main lines of models: one for commercial or data processing use, and another one for engineering and scientific use. The two lines were largely incompatible. This all changed with the introduction of the System/360 (S/360) in April of 1964. The System/360 was a single series of compatible models, for both commercial and scientific use. The System/360 later evolved into the System/370, the System/390, and most recently the zSeries.
System/360 (the "360 degree", i.e., "all-around" computer system) incorporated into a single architecture features which had previously been present on only the commercial (decimal arithmetic, for example, or byte addressing) or the technical (floating point arithmetic) lines of machines.¹ The System/360 was also the first computer architecture in wide use to include dedicated hardware provisions for the use of operating systems. Among these were the notion of supervisor and application mode programs and instructions, as well as built-in memory protection facilities.²
(¹ Some of the arithmetics units and addressing features were optional on some models of the System/360.)
(² Hardware memory protection was provided to protect the operating system from the user programs (tasks), and the user tasks from each other.)
Notable pre-System/360 IBM mainframes include:
Operating systems The primary operating systems in use on today's IBM mainframes include MVS (later called OS/390 or z/OS), VM/CMS (later called z/VM), VSE, TPF, and, most recently, GNU/Linux. (A few systems also remain that run MUSIC/SP.) Previous operating systems for the System/360 family and its successors have included OS/360 (with PCP, MFT, and MVT), BOS, TOS, DOS, and SVS. The System/370, System/390 and zSeries hardware can be emulated using the freely available Hercules emulator which runs under GNU/Linux and Microsoft Windows. The original OS/360 have also been released for free use, as have earlier versions of MVS and VM/CMS.
See also
References - Prasad, Nallur (1994). IBM Mainframes: Architecture and Design. 2nd ed. McGraw-Hill Osborne Media. ISBN 0070506914.
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