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HISTORY From . Later IBM provided compilers for the newly developed higher-level Programming Language s Fortran and Cobol . The need to make the most efficient use of these multi-million dollar machines led to the introduction of simple Operating System s, or job monitors. The two categories, scientific and commercial, generally used common peripherals but had completely different Instruction Set s, and there were incompatibilities even within each category. As software became more complex and important, the cost of supporting it on so many different designs became burdensome. All that changed with the announcement of the System/360 (S/360) in April, 1964. The System/360 was a single series of compatible models for both commercial and scientific use. The number " 360 " suggested a "360 Degree ," or "all-around" computer system. System/360 incorporated features which had previously been present on only either the commercial line (such as decimal arithmetic and byte addressing) or the technical line (such as Floating Point arithmetic).Some of the arithmetic units and addressing features were optional on some models of the System/360. However, models were upward compatible and most were also downward compatible. The System/360 was also the first computer in wide use to include dedicated hardware provisions for the use of Operating System s. Among these were supervisor and application mode programs and instructions, as well as built-in memory protection facilities.Hardware memory protection was provided to protect the operating system from the user programs (tasks) and the user tasks from each other. The new machine also had a larger Address Space than the older mainframes, 24 bits vs. a typical 18 bits. The System/360 later evolved into the System/370 , the System/390 , the ZSeries , and the System Z9 . Prior to System/360, IBM also sold computers smaller in scale, though still large and expensive by modern standards. These included:
IBM had difficulty getting customers to upgrade from the smaller machines to the mainframes because so much software had to be rewritten. The 7010 was introduced in 1962 as a mainframe-sized 1410. The smaller models in the System/360 line (e.g. the 360/30) were intended to replace the 1400 series while providing an easier upgrade path to the larger 360s. A desk size machine with a different instruction set, the IBM 1130 , was released to address the 1620's niche. It was mostly programmed in Fortran, which was relatively easy to adapt to larger machines when necessary. The second generation products were a mainstay of IBM's business and IBM continued to make them for several years after the introduction of the System/360. (Some IBM 7094 s remained in service into the 1980s.) To smooth the transition from second generation to the new line, IBM used the 360's Microprogramming capability to emulate the more popular older models. Thus 360/30s with this added cost feature could run 1401 programs and the larger 360/65s could run 7094 programs. To run old programs, the 360 had to be halted and restarted in emulation mode. Many customers kept using their old software and one of the features of the later System/370 was the ability to switch to emulation mode and back under operating system control. SOFTWARE Operating systems The primary Operating System s in use on IBM mainframes include Z/OS (which followed MVS and OS/390 ), Z/VM (previously VM/CMS ), Z/VSE , Z/TPF , and Linux On ZSeries . A few systems still run MUSIC/SP , another operating system. Previous operating systems for the System/360 family and its successors included OS/360 (with PCP, MFT, and MVT), BOS, TOS, DOS , and SVS. There are software-based emulators for the System/370 , System/390 , ZSeries , and System Z9 hardware, including FLEX-ES and the freely available Hercules Emulator which runs under Linux and Microsoft Windows . The original OS/360 and early MVS and VM/CMS versions have been released for free use. Middleware IBM mainframes run all the major enterprise Transaction Processing environments and Database s, including CICS , IMS , WebSphere Application Server, DB2 , and Oracle . In many cases these Software subsystems can run on more than one mainframe operating system. SEE ALSO REFERENCES
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