| History ofIBM mainframes, 1952–present |
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IBM mainframes are large computer systems produced byIBM since 1952. During the 1960s and 1970s, IBM dominated the computer market with the7000 series and the laterSystem/360, followed by theSystem/370. Currentmainframe computers in IBM's line of business computers are developments of the basic design of the System/360.
From 1952 into the late 1960s, IBM manufactured and marketed several large computer models, known as theIBM 700/7000 series. Thefirst-generation 700s were based onvacuum tubes, while the later, second-generation 7000s usedtransistors. These machines established IBM's dominance inelectronic data processing ("EDP"). IBM had two model categories: one (701, 704, 709, 7030, 7090, 7094, 7040, 7044) for engineering and scientific use, and one (702, 705, 705-II, 705-III, 7080, 7070, 7072, 7074, 7010) for commercial or data processing use. The two categories, scientific and commercial, generally used common peripherals but had completely differentinstruction sets, and there were incompatibilities even within each category.
IBM initially sold its computers without any software, expecting customers to write their own; programs were manually initiated, one at a time. Later, IBM providedcompilers for the newly developed higher-levelprogramming languagesFortran,COMTRAN and laterCOBOL. The firstoperating systems for IBM computers were written by IBM customers who did not wish to have their very expensive machines (US$2M in the mid-1950s) sitting idle while operators set up jobs manually. These first operating systems were essentially scheduled work queues. It is generally thought the first operating system used for real work wasGM-NAA I/O, produced byGeneral Motors' Research division in 1956. IBM enhanced one of GM-NAA I/O's successors, theSHARE Operating System, and provided it to customers under the nameIBSYS.[1][2] As software became more complex and important, the cost of supporting it on so many different designs became burdensome, and this was one of the factors which led IBM to developSystem/360 and its operating systems.[3]
Thesecond generation (transistor-based) products were a mainstay of IBM's business and IBM continued to make them for several years after the introduction of the System/360. (SomeIBM 7094s remained in service into the 1980s.)
Prior to System/360, IBM also sold computers smaller in scale that were not considered mainframes, though they were still bulky 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 later Systems 360 and 370 could emulate the 1400 machines. A desk-size machine with a different instruction set, theIBM 1130, was released concurrently with the System/360 to address the niche occupied by the 1620. It used the sameEBCDIC character encoding as the 360 and was mostly programmed inFortran, which was relatively easy to adapt to larger machines when necessary.
IBM also introduced smaller machines after S/360. These included:
Midrange computer is a designation used by IBM for a class of computer systems which fall in between mainframes and microcomputers.
IBM announced the System/360 (S/360) line of mainframes in April 1964.[4] The System/360 was a single series of compatible models for both commercial and scientific use. The number "360" suggested a "360degree," 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 engineering and scientific line (such asfloating-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 ofoperating systems. 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 user tasks from each other. The new machine also had a largeraddress space than the older mainframes, 24 bits addressing 8-bit bytes vs. a typical 18 bits addressing 36-bit words.
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. To smooth the transition from the second generation to the new line, IBM used the 360'smicroprogramming 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.
Operating systems for the System/360 family includedOS/360 (with PCP, MFT, andMVT),BOS/360,TOS/360, andDOS/360.
The System/360 later evolved into theSystem/370, theSystem/390, and the64-bitzSeries, System z, and zEnterprise machines. System/370 introducedvirtual memory capabilities in all models other than the first System/370 models; theOS/VS1 variant of OS/360 MFT, theOS/VS2 (SVS) variant of OS/360 MVT, and the DOS/VS variant of DOS/360 were introduced to use the virtual memory capabilities, followed byMVS, which, unlike the earlier virtual-memory operating systems, ran separate programs in separate address spaces, rather than running all programs in a single virtual address space. The virtual memory capabilities also allowed the system to supportvirtual machines; theVM/370hypervisor would run one or more virtual machines running either standard System/360 or System/370 operating systems or the single-userConversational Monitor System (CMS). Atime-sharing VM system could run multiple virtual machines, one per user, with each virtual machine running an instance of CMS.
TheIBM Z family, introduced in 2000 with the z900, supportsz/Architecture, which extends the architecture used by the System/390 mainframes to 64 bits.
The different processors on current IBM mainframes are:
These are essentially identical, but distinguished for software cost control: all but CP are slightly restricted[a] such they cannot be used to run arbitrary operating systems, and thus do not count in software licensing costs (which are typically based on the number of CPs).[5]There are other supporting processors typically installed inside mainframes such ascryptographic accelerators (CryptoExpress), theOSA-Express networking processor, andFICON Express disk I/O processors.
Software to allow users to run "traditional" workloads on zIIPs and zAAPs was briefly marketed by Neon Enterprise Software as "zPrime" but was withdrawn from the market in 2011 after a lawsuit by IBM.[6]
The primaryoperating systems in use on current IBM mainframes includez/OS (which followedMVS/ESA andOS/390 in theOS/360 lineage),z/VM (which followedVM/ESA and VM/XA SP in theCP-40 lineage),z/VSE (which is in theDOS/360 lineage),z/TPF (a successor of Transaction Processing Facility in theAirlines Control Program lineage), andLinux on IBM Z (e.g.,Debian,Red Hat Enterprise Linux,SUSE Linux Enterprise Server). Some systems runMUSIC/SP, as well asUTS (Mainframe UNIX). In October 2008, Sine Nomine Associates introducedOpenSolaris on System z; it has since been discontinued.
Current IBM mainframes run all the major enterprisetransaction processing environments anddatabases, includingCICS,IMS,WebSphere Application Server,IBM Db2, andOracle. In many cases thesesoftware subsystems can run on more than one mainframe operating system.
There are software-based emulators for the System/370, System/390, and System z hardware, includingFLEX-ES, which runs underUnixWare orLinux,[7] and the freely availableHercules, which runs underLinux,FreeBSD,Solaris,macOS andMicrosoft Windows.IBM offers an emulator called zPDT (System z Personal Development Tool) which runs on Linux onx86-64 machines.[8]
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