Editing IBM mainframe

{{short description|Large computer systems produced by IBM since 1952}}
{{Use American English|date=March 2023}}
{{Use mdy dates|date=March 2023}}
{{IBM mainframes}}

'''IBM mainframes''' are large computer systems produced by [[IBM]] since 1952. During the 1960s and 1970s, IBM dominated the computer market with the [[IBM 700/7000 series|7000 series]] and the later [[System/360]], followed by the [[System/370]]. Current [[mainframe computer]]s in IBM's line of business computers are developments of the basic design of the System/360.

==First and second generation==
[[File:IBM Electronic Data Processing Machine - GPN-2000-001881.jpg|thumb|right| IBM 704 mainframe at [[National Advisory Committee for Aeronautics|NACA]] in 1957]]

From 1952 into the late 1960s, IBM manufactured and marketed several large computer models, known as the [[IBM 700/7000 series]]. The [[Vacuum-tube computer|first-generation]] 700s were based on [[vacuum tube]]s, while the later, second-generation 7000s used [[transistor]]s. These machines established IBM's dominance in [[electronic 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 different [[instruction set]]s, 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 provided [[compilers]] for the newly developed higher-level [[programming language]]s [[Fortran]], [[COMTRAN]] and later [[COBOL]]. The first [[operating 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 was [[GM-NAA I/O]], produced by [[General Motors]]' Research division in 1956. IBM enhanced one of GM-NAA I/O's successors, the [[SHARE Operating System]], and provided it to customers under the name [[IBSYS]].<ref name="frobeniusIBSYS">{{cite web| url = http://www.frobenius.com/ibsys.htm| title = IBM 7090/94 IBSYS Operating System| archive-url = https://web.archive.org/web/20210424184903/http://www.frobenius.com/ibsys.htm| archive-date = April 24, 2021}}</ref><ref name="UnisysHistNewsletterV1N3">{{cite journal
 | last         = Gray
 | first        = George
 | date         = March 1999
 | title        = EXEC II
 | periodical   = Unisys History Newsletter
 | volume       = 1
 | issue        = 3
 | url          = https://wiki.cc.gatech.edu/folklore/index.php/EXEC_II
 | archive-url  = https://web.archive.org/web/20170809171206/https://wiki.cc.gatech.edu/folklore/index.php/EXEC_II
 | archive-date = August 9, 2017}}</ref> 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 develop [[System/360]] and its operating systems.<ref name="Boyer360Revolution">{{cite web
 |     title = The 360 Revolution
 |     author = Chuck Boyer
 |     url = http://www.ibm.com/servers/eserver/au/zseries/download/360revolution_040704.pdf
 |     publisher = IBM
 |     access-date = December 22, 2020
 |     archive-date = July 1, 2023
 |     archive-url = https://web.archive.org/web/20230701114010/https://www.ibm.com/servers
 |     url-status = live
 }}</ref>

The [[Transistor computer|second 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. (Some [[IBM 7094]]s remained in service into the 1980s.)

==Smaller machines==
[[File:IBM 1401 signal tracing at CHM.jpg|thumb|right|IBM 1401 undergoing restoration at the [[Computer History Museum]]]]

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 650]] (vacuum tube logic, [[decimal architecture]], [[drum memory]], business and scientific)
* [[IBM 305 RAMAC]] (vacuum tube logic, first computer with [[disk storage]]; ''see:'' [[Early IBM disk storage]])
* [[IBM 1400 series]] (business data processing; very successful and many 1400 peripherals were used with the 360s)
* [[IBM 1620]] (decimal architecture, engineering, scientific, and education)

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, the [[IBM 1130]], was released concurrently with the System/360 to address the niche occupied by the 1620. It used the same [[EBCDIC]] character encoding as the 360 and was mostly programmed in [[Fortran]], which was relatively easy to adapt to larger machines when necessary.

IBM also introduced smaller machines after S/360. These included:
* [[IBM System/7]] (semiconductor memory, process control, incompatible replacement for [[IBM 1800]]
* [[IBM Series/1]]
* [[IBM 3790]]
* [[IBM 8100]]
* [[IBM System/3]] (Introduced 96 column card)

[[IBM midrange computer|''Midrange computer'']] is a designation used by IBM for a class of computer systems which fall in between mainframes and microcomputers.

==IBM System/360==
{{main|IBM System/360}}

[[File:IBM system 360-50 console - MfK Bern.jpg|thumb|right|IBM System/360 Model 50]]

IBM announced the System/360 (S/360) line of mainframes in April 1964.<ref>{{cite web| url = http://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR360.html| title = IBM Archives: System/360 Announcement| website = [[IBM]]| date = January 23, 2003| access-date = December 22, 2020| archive-date = January 2, 2021| archive-url = https://web.archive.org/web/20210102231457/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR360.html| url-status = live}}</ref> The System/360 was a single series of compatible models for both commercial and scientific use. The number "[[360 (number)|360]]" suggested a "360 [[degree (angle)|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 engineering and scientific 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 user tasks from each other. The new machine also had a larger [[address 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'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.

Operating systems for the System/360 family included [[OS/360]] (with PCP, MFT, and [[Multiprogramming with a Variable number of Tasks|MVT]]), [[BOS/360]], [[TOS/360]], and [[DOS/360]].

The System/360 later evolved into the [[System/370]], the [[System/390]], and the [[64-bit]] [[IBM System z|zSeries, System z, and zEnterprise]] machines. System/370 introduced [[virtual memory]] capabilities in all models other than the first System/370 models; the [[OS/VS1]] variant of OS/360 MFT, the [[OS/VS2 (SVS)]] variant of OS/360 MVT, and the DOS/VS variant of DOS/360 were introduced to use the virtual memory capabilities, followed by [[MVS]], 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 support [[virtual machine]]s; the [[VM (operating system)|VM/370]] [[hypervisor]] would run one or more virtual machines running either standard System/360 or System/370 operating systems or the single-user [[Conversational Monitor System]] (CMS). A [[time-sharing]] VM system could run multiple virtual machines, one per user, with each virtual machine running an instance of CMS.

==Today's systems==
{{main|IBM Z}}

[[File:Z800 2066 JKU.jpeg|thumb|right|IBM System z800]]

The [[IBM Z]] family, introduced in 2000 with the z900, supports [[z/Architecture]], which extends the architecture used by the System/390 mainframes to 64 bits.

===Processor units===
The different processors on current IBM mainframes are:
* CP, [[central processor]]: general-purpose processor
* IFL, [[Integrated Facility for Linux]]: dedicated to [[Linux]] OSes (optionally under [[z/VM]])
* ICF, Integrated [[Coupling Facility]]: designed to support [[IBM Parallel Sysplex|Parallel Sysplex]] operations
* SAP, System Assist Processor: designed to handle various system accounting, management, and [[I/O channel]] operations
* [[zAAP]], System z Application Assist Processor: currently limited to run only [[Java (programming language)|Java]] and [[XML]] processing
* [[zIIP]], System z Integrated Information Processor: dedicated to run specific workloads including [[IBM Db2]], [[XML]], and [[IPSec]]

These are essentially identical, but distinguished for software cost control: all but CP are slightly restricted{{efn|All supported IBM operating systems test the type of processor they are running on and restrict usage in accordance with license terms.}} 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).<ref>{{cite web|url=http://publib.boulder.ibm.com/infocenter/zos/basics/topic/com.ibm.zos.zmainframe/zmainframe_book.pdf|title=Mainframe concepts (page 31)|author=IBM corp.|year=2005|access-date=May 5, 2012|archive-date=July 8, 2012|archive-url=https://web.archive.org/web/20120708195859/http://publib.boulder.ibm.com/infocenter/zos/basics/topic/com.ibm.zos.zmainframe/zmainframe_book.pdf|url-status=live}}</ref>
There are other supporting processors typically installed inside mainframes such as [[cryptographic]] accelerators ([[CryptoExpress]]), the [[OSA-Express]] networking processor, and [[FICON]] 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.<ref>{{cite web|last=Radding|first=Alan|title=Bye bye zPrime on System z|date=June 6, 2011|url=http://dancingdinosaur.wordpress.com/2011/06/06/bye-bye-zprime-on-system-z/|publisher=DancingDinosaur|access-date=May 5, 2012|archive-date=June 30, 2012|archive-url=https://web.archive.org/web/20120630214501/http://dancingdinosaur.wordpress.com/2011/06/06/bye-bye-zprime-on-system-z/|url-status=live}}</ref>

===Operating systems===
The primary [[operating system]]s in use on current IBM mainframes include [[z/OS]] (which followed [[MVS#MVS/ESA|MVS/ESA]] and [[OS/390]] in the [[OS/360 and successors|OS/360]] lineage), [[z/VM]] (which followed [[VM (operating system)|VM/ESA]] and VM/XA SP in the [[CP/CMS|CP-40]] lineage), [[z/VSE]] (which is in the [[DOS/360 and successors|DOS/360 lineage]]), [[z/TPF]] (a successor of Transaction Processing Facility in the [[Airlines Control Program]] lineage), and [[Linux on IBM Z]] (e.g., [[Debian]], [[Red Hat Enterprise Linux]], [[SUSE Linux Enterprise Server]]). Some systems run [[MUSIC/SP]], as well as [[UTS (Mainframe UNIX)]]. In October 2008, Sine Nomine Associates introduced [[OpenSolaris on System z]]; it has since been discontinued.

===Middleware===
Current IBM mainframes run all the major enterprise [[transaction processing]] environments and [[database]]s, including [[CICS]], [[Information Management System|IMS]], [[WebSphere]] Application Server, [[IBM Db2]], and [[Oracle Database|Oracle]]. In many cases these [[software]] subsystems can run on more than one mainframe operating system.

===Emulators===
There are software-based emulators for the System/370, System/390, and System z hardware, including [[FLEX-ES]], which runs under [[UnixWare]] or [[Linux]],<ref>{{cite web|url=http://www.funsoft.com/technical.html|title=Technical Overview: FLEX-ES|access-date=May 8, 2015|archive-date=May 18, 2015|archive-url=https://web.archive.org/web/20150518070835/http://www.funsoft.com/technical.html|url-status=live}}</ref> and the freely available [[Hercules (emulator)|Hercules]], which runs under [[Linux]], [[FreeBSD]], [[Solaris (operating system)|Solaris]], [[macOS]] and [[Microsoft Windows]].
IBM offers an emulator called zPDT (System z Personal Development Tool) which runs on Linux on [[x86-64]] machines.<ref>{{cite web|url=https://www-304.ibm.com/partnerworld/wps/servlet/ContentHandler/pw_com_zpdt|title=IBM System z Personal Development Tool|publisher=IBM|access-date=January 27, 2016|archive-date=March 4, 2016|archive-url=https://web.archive.org/web/20160304051831/https://www-304.ibm.com/partnerworld/wps/servlet/ContentHandler/pw_com_zpdt|url-status=live}}</ref>

==See also==
* [[List of IBM products]]
* [[Amdahl Corporation]]
* [[IBM midrange computer]]
* [[IBM LinuxONE]]
* [[IBM Secure Service Container]]
* [[Input/Output Configuration Program]]

==Notes==
{{Notelist}}

==References==
{{Reflist}}

==Further reading==
* {{cite book
 | last            = Bashe
 | first           = Charles J.
 | title           = IBM's Early Computers
 | publisher       = MIT
 | year            = 1986
 | isbn            = 0-262-02225-7
 | display-authors = etal
 | url-access      = registration
 | url             = https://archive.org/details/ibmsearlycompute00bash}}
* Prasad, Nallur and Savit, Jeffrey (1994). ''IBM Mainframes: Architecture and Design'', 2nd ed. McGraw-Hill Osborne Media. {{ISBN|0-07-050691-4}}.
* {{cite book
 | last       = Pugh
 | first      = Emerson W.
 | title      = IBM's 360 and Early 370 Systems
 | url        = https://archive.org/details/ibms360early370s0000pugh
 | url-access = registration
 | publisher  = MIT
 | year       = 1991
 | isbn       = 0-262-16123-0|display-authors=etal}}

==External links==
{{Commons category|IBM mainframe computers}}
* [https://www.ibm.com/it-infrastructure/z Official IBM mainframe page (IBM Z)]
* [https://ibmmainframes.com IBM Mainframe Resources & Forum]
* [https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_intro.html IBM Archives: IBM Mainframes] 
* [https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_FT1.html IBM Archives: IBM Mainframe Family tree & chronology] 
* [https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_album.html IBM Archives: IBM Mainframe album]

{{IBM}}
{{Mainframes}}

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[[Category:IBM mainframe computers| ]]
[[Category:Computer-related introductions in 1952]]