Wed . 19 Jun 2019

Mainframe computer

mainframe computer, mainframe computer images
Mainframe computers colloquially referred to as "big iron"1 are computers used primarily by large organizations for critical applications, bulk data processing, such as census, industry and consumer statistics, enterprise resource planning, and transaction processing

The term originally referred to the large cabinets called "main frames" that housed the central processing unit and main memory of early computers23 Later, the term was used to distinguish high-end commercial machines from less powerful units4 Most large-scale computer system architectures were established in the 1960s, but continue to evolve


  • 1 Definition
  • 2 Characteristics
  • 3 Market
  • 4 History
  • 5 Differences from supercomputers
  • 6 See also
  • 7 Notes
  • 8 References
  • 9 External links


Modern mainframe design is generally less defined by single-task computational speed typically defined as MIPS rate or FLOPS in the case of floating point calculations, and more by:

  • Redundant internal engineering resulting in high reliability and security
  • Extensive input-output facilities with the ability to offload to separate engines
  • Strict backward compatibility with older software
  • High hardware and computational utilization rates through virtualization to support massive throughput

Their high stability and reliability enables these machines to run uninterrupted for decades

Software upgrades usually require setting up the operating system or portions thereof, and are non-disruptive only when using virtualizing facilities such as IBM's z/OS and Parallel Sysplex, or Unisys's XPCL, which support workload sharing so that one system can take over another's application while it is being refreshed Mainframes are defined by high availability, one of the main reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic The term reliability, availability and serviceability RAS is a defining characteristic of mainframe computers Proper planning and implementation is required to exploit these features, and if improperly implemented, may serve to inhibit the benefits provided In addition, mainframes are more secure than other computer types: the NIST vulnerabilities database, US-CERT, rates traditional mainframes such as IBM zSeries, Unisys Dorado and Unisys Libra as among the most secure with vulnerabilities in the low single digits as compared with thousands for Windows, Unix, and Linux5

In the late 1950s, most mainframes had no explicitly interactive interface, but only accepted sets of punched cards, paper tape, or magnetic tape to transfer data and programs They operated in batch mode to support back office functions such as payroll and customer billing, much of which was based on repeated tape-based sorting and merging operations followed by a print run to preprinted continuous stationery In cases where interactive terminals were supported, these were used almost exclusively for applications eg airline booking rather than program development Typewriter and Teletype devices were also common control consoles for system operators through the 1970s, although ultimately supplanted by keyboard/display devices

By the early 1970s, many mainframes acquired interactive user interfacesNB 1 and operated as timesharing computers, supporting hundreds of users simultaneously along with batch processing Users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software By the 1980s, many mainframes supported graphical terminals, and terminal emulation, but not graphical user interfaces This format of end-user computing reached mainstream obsolescence in the 1990s due to the advent of personal computers provided with GUIs After 2000, most modern mainframes have partially or entirely phased out classic "green screen" terminal access for end-users in favour of Web-style user interfacescitation needed

The infrastructure requirements were drastically reduced during the mid-1990s, when CMOS mainframe designs replaced the older bipolar technology IBM claimed that its newer mainframes could reduce data center energy costs for power and cooling, and that they could reduce physical space requirements compared to server farms6


Inside an IBM System z9 mainframe

Modern mainframes can run multiple different instances of operating systems at the same time This technique of virtual machines allows applications to run as if they were on physically distinct computers In this role, a single mainframe can replace higher-functioning hardware services available to conventional servers While mainframes pioneered this capability, virtualization is now available on most families of computer systems, though not always to the same degree or level of sophistication7

Mainframes can add or hot swap system capacity without disrupting system function, with specificity and granularity to a level of sophistication not usually available with most server solutionscitation needed Modern mainframes, notably the IBM zSeries, System z9 and System z10 servers, offer two levels of virtualization: logical partitions LPARs, via the PR/SM facility and virtual machines via the z/VM operating system Many mainframe customers run two machines: one in their primary data center, and one in their backup data center—fully active, partially active, or on standby—in case there is a catastrophe affecting the first building Test, development, training, and production workload for applications and databases can run on a single machine, except for extremely large demands where the capacity of one machine might be limiting Such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages In practice many customers use multiple mainframes linked either by Parallel Sysplex and shared DASD in IBM's case,citation needed or with shared, geographically dispersed storage provided by EMC or Hitachi

Mainframes are designed to handle very high volume input and output I/O and emphasize throughput computing Since the late-1950s,NB 2 mainframe designs have included subsidiary hardwareNB 3 called channels or peripheral processors which manage the I/O devices, leaving the CPU free to deal only with high-speed memory It is common in mainframe shops to deal with massive databases and files Gigabyte to terabyte-size record files are not unusual8 Compared to a typical PC, mainframes commonly have hundreds to thousands of times as much data storage online,9 and can access it reasonably fast Other server families also offload I/O processing and emphasize throughput computing

Mainframe return on investment ROI, like any other computing platform, is dependent on its ability to scale, support mixed workloads, reduce labor costs, deliver uninterrupted service for critical business applications, and several other risk-adjusted cost factors

Mainframes also have execution integrity characteristics for fault tolerant computing For example, z900, z990, System z9, and System z10 servers effectively execute result-oriented instructions twice, compare results, arbitrate between any differences through instruction retry and failure isolation, then shift workloads "in flight" to functioning processors, including spares, without any impact to operating systems, applications, or users This hardware-level feature, also found in HP's NonStop systems, is known as lock-stepping, because both processors take their "steps" ie instructions together Not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processingcitation needed


IBM is a major manufacturer in the mainframe market Unisys manufactures ClearPath Libra mainframes, based on earlier Burroughs products and ClearPath Dorado mainframes based on Sperry Univac OS 1100 product lines In 2002, Hitachi co-developed the zSeries z800 with IBM to share expenses, but subsequently the two companies have not collaborated on new Hitachi models Hewlett-Packard sells its unique NonStop systems, which it acquired with Tandem Computers and which some analysts classify as mainframes Groupe Bull's DPS, Fujitsu formerly Siemens BS2000, and Fujitsu-ICL VME mainframes are still available in Europe Fujitsu, Hitachi, and NEC the "JCMs" still maintain mainframe hardware businesses in the Japanese market1011

The amount of vendor investment in mainframe development varies with market share Fujitsu and Hitachi both continue to use custom S/390-compatible processors, as well as other CPUs including POWER and Xeon for lower-end systems Bull uses a mixture of Itanium and Xeon processors NEC uses Xeon processors for its low-end ACOS-2 line, but develops the custom NOAH-6 processor for its high-end ACOS-4 series IBM continues to pursue a different business strategy of mainframe investment and growthcitation needed IBM has its own large research and development organization designing new, homegrown CPUs, including mainframe processors such as 2012's 55 GHz six-core zEC12 mainframe microprocessor Unisys produces code compatible mainframe systems that range from laptops to cabinet sized mainframes that utilize homegrown CPUs as well as Xeon processors IBM is rapidly expanding its software business, including its mainframe software portfolio, to seek additional revenue and profits12

Furthermore, there exists a market for software applications to manage the performance of mainframe implementations In addition to IBM, significant players in this market include BMC,13 Compuware,1415 and CA Technologies16


An IBM 704 mainframe 1964

Several manufacturers produced mainframe computers from the late 1950s through the 1970s The group of manufacturers was first known as "IBM and the Seven Dwarfs":17:p83 usually Burroughs, UNIVAC, NCR, Control Data, Honeywell, General Electric and RCA, although some lists varied Later, with the departure of General Electric and RCA, it was referred to as IBM and the BUNCH IBM's dominance grew out of their 700/7000 series and, later, the development of the 360 series mainframes The latter architecture has continued to evolve into their current zSeries mainframes which, along with the then Burroughs and Sperry now Unisys MCP-based and OS1100 mainframes, are among the few mainframe architectures still extant that can trace their roots to this early period While IBM's zSeries can still run 24-bit System/360 code, the 64-bit zSeries and System z9 CMOS servers have nothing physically in common with the older systems Notable manufacturers outside the US were Siemens and Telefunken in Germany, ICL in the United Kingdom, Olivetti in Italy, and Fujitsu, Hitachi, Oki, and NEC in Japan The Soviet Union and Warsaw Pact countries manufactured close copies of IBM mainframes during the Cold War; the BESM series and Strela are examples of an independently designed Soviet computer

Shrinking demand and tough competition started a shakeout in the market in the early 1970s—RCA sold out to UNIVAC and GE sold its business to Honeywell; in the 1980s Honeywell was bought out by Bull; UNIVAC became a division of Sperry, which later merged with Burroughs to form Unisys Corporation in 1986

During the 1980s, minicomputer-based systems grew more sophisticated and were able to displace the lower-end of the mainframes These computers, sometimes called departmental computers were typified by the DEC VAX

In 1991, AT&T Corporation briefly owned NCR During the same period, companies found that servers based on microcomputer designs could be deployed at a fraction of the acquisition price and offer local users much greater control over their own systems given the IT policies and practices at that time Terminals used for interacting with mainframe systems were gradually replaced by personal computers Consequently, demand plummeted and new mainframe installations were restricted mainly to financial services and government In the early 1990s, there was a rough consensus among industry analysts that the mainframe was a dying market as mainframe platforms were increasingly replaced by personal computer networks InfoWorld's Stewart Alsop famously predicted that the last mainframe would be unplugged in 1996; in 1993, he cited Cheryl Currid, a computer industry analyst as saying that the last mainframe "will stop working on December 31, 1999",18 a reference to the anticipated Year 2000 problem Y2K

That trend started to turn around in the late 1990s as corporations found new uses for their existing mainframes and as the price of data networking collapsed in most parts of the world, encouraging trends toward more centralized computing The growth of e-business also dramatically increased the number of back-end transactions processed by mainframe software as well as the size and throughput of databases Batch processing, such as billing, became even more important and larger with the growth of e-business, and mainframes are particularly adept at large scale batch computing Another factor currently increasing mainframe use is the development of the Linux operating system, which arrived on IBM mainframe systems in 1999 and is typically run in scores or hundreds of virtual machines on a single mainframe Linux allows users to take advantage of open source software combined with mainframe hardware RAS Rapid expansion and development in emerging markets, particularly People's Republic of China, is also spurring major mainframe investments to solve exceptionally difficult computing problems, eg providing unified, extremely high volume online transaction processing databases for 1 billion consumers across multiple industries banking, insurance, credit reporting, government services, etc In late 2000, IBM introduced 64-bit z/Architecture, acquired numerous software companies such as Cognos and introduced those software products to the mainframe IBM's quarterly and annual reports in the 2000s usually reported increasing mainframe revenues and capacity shipments However, IBM's mainframe hardware business has not been immune to the recent overall downturn in the server hardware market or to model cycle effects For example, in the 4th quarter of 2009, IBM's System z hardware revenues decreased by 27% year over year But MIPS shipments increased 4% per year over the past two years19 Alsop had himself photographed in 2000, symbolically eating his own words "death of the mainframe"20

In 2012, NASA powered down its last mainframe, an IBM System z921 However, IBM's successor to the z9, the z10, led a New York Times reporter to state four years earlier that "mainframe technology — hardware, software and services — remains a large and lucrative business for IBM, and mainframes are still the back-office engines behind the world’s financial markets and much of global commerce"22 As of 2010update, while mainframe technology represented less than 3% of IBM's revenues, it "continued to play an outsized role in Big Blue's results"23

In 2015, IBM launched its most recent generation mainframe, the IBM z1324

Differences from supercomputersedit

A supercomputer is a computer that is at the frontline of current processing capacity, particularly speed of calculation Supercomputers are used for scientific and engineering problems high-performance computing which are data crunching and number crunching,25 while mainframes are used for transaction processing The differences are as follows:

  • Mainframes are built to be reliable for transaction processing measured by TPC-metrics; not used or very helpful for most supercomputing applications as it is commonly understood in the business world: a commercial exchange of goods, services, or moneycitation needed A typical transaction, as defined by the Transaction Processing Performance Council,26 would include the updating to a database system for such things as inventory control goods, airline reservations services, or banking money A transaction could refer to a set of operations including disk read/writes, operating system calls, or some form of data transfer from one subsystem to another This operation doesn't count toward the processing power of a computer Transaction processing is not exclusive to mainframes but also used in the performance of microprocessor-based servers and online networks
  • Supercomputers are measured in floating point operations per second FLOPS27 or in traversed edges per second or TEPS;28 metrics that are not very meaningful for mainframe applications; while mainframes are sometimes approximately measured in millions of instructions per second MIPS,29 a metric not used on supercomputers; as not very helpful, it's arguably neither for mainframes to measure real performance of the transaction processing goal, but such or similar sub-component of it, may be used for billing purposes Examples of integer operations the instructions counted by MIPS include adding numbers together, checking values or moving data around in memory while moving information to and from storage, so-called I/O is most helpful for mainframes; and within memory, only helping indirectly Floating point operations are mostly addition, subtraction, and multiplication of binary floating point in supercomputers; measured by FLOPS with enough digits of precision to model continuous phenomena such as weather prediction and nuclear simulations only recently standardized decimal floating point, not used in supercomputers, are appropriate from monetary values such as those useful for mainframe applications In terms of computational ability, supercomputers are more powerful30

In 2007,31 an amalgamation of the different technologies and architectures for supercomputers and mainframes has led to the so-called gameframe

See alsoedit

  • Computer types
  • Failover
  • Gameframe
  • Channel I/O
  • Cloud computing


  1. ^ In some cases these had been introduced in the 1960s, but their deployment became more common in the 1970s
  2. ^ Eg, the IBM 709 had channels in 1958
  3. ^ sometimes computers, sometimes more limited


  1. ^ "IBM preps big iron fiesta" The Register July 20, 2005 
  2. ^ "mainframe, n" Oxford English Dictionary on-line ed 
  3. ^ Ebbers, Mike; O’Brien, W; Ogden, B 2006 "Introduction to the New Mainframe: z/OS Basics" PDF IBM International Technical Support Organization Retrieved 2007-06-01 
  4. ^ Beach, Thomas E "Computer Concepts and Terminology: Types of Computers" Retrieved November 17, 2012 
  5. ^ "National Vulnerability Database" Retrieved September 20, 2011 
  6. ^ "Get the facts on IBM vs the Competition- The facts about IBM System z "mainframe"" IBM Retrieved December 28, 2009 
  7. ^ "Emulation or Virtualization" 
  8. ^ "Largest Commercial Database in Winter Corp TopTen Survey Tops One Hundred Terabytes" Press release Retrieved 2008-05-16 
  9. ^ "Improvements in Mainframe Computer Storage Management Practices and Reporting Are Needed to Promote Effective and Efficient Utilization of Disk Resources" Between October 2001 and September 2005, the IRS’ mainframe computer disk storage capacity increased from 79 terabytes to 1685 terabytes 
  10. ^ GlobalServer : Fujitsu Global Fujitsucom Retrieved on 2013-07-17
  11. ^ エンタープライズサーバAP8800E:日立 Hitachicojp Retrieved on 2013-07-17
  12. ^ "IBM Opens Latin America's First Mainframe Software Center" Enterprise Networks and Servers August 2007 
  13. ^ "Mainframe Automation Management" Retrieved 26 October 2012 
  14. ^ "Mainframe Modernization" Retrieved 26 October 2012 
  15. ^ "Automated Mainframe Testing & Auditing" Retrieved 26 October 2012 
  16. ^ "CA Technologies" 
  17. ^ Bergin, Thomas J ed 2000 50 Years of Army Computing: From ENIAC to MSRC DIANE Publishing ISBN 0-9702316-1-X 
  18. ^ Alsop, Stewart Mar 8, 1993 "IBM still has brains to be player in client/server platforms" InfoWorld Retrieved Dec 26, 2013 
  19. ^ "IBM 4Q2009 Financial Report: CFO's Prepared Remarks" PDF IBM January 19, 2010 
  20. ^ "Stewart Alsop eating his words" Computer History Museum Retrieved Dec 26, 2013 
  21. ^ Cureton, Linda 11 February 2012 The End of the Mainframe Era at NASA NASA Retrieved 31 January 2014 
  22. ^ Lohr, Steve March 23, 2008 "Why Old Technologies Are Still Kicking" The New York Times Retrieved Dec 25, 2013 
  23. ^ Ante, Spencer E July 22, 2010 "IBM Calculates New Mainframes Into Its Future Sales Growth" The Wall Street Journal Retrieved Dec 25, 2013 
  24. ^ Press, Gil "From IBM Mainframe Users Group To Apple 'Welcome IBM Seriously': This Week In Tech History" Forbes Retrieved 2016-10-07 
  25. ^ High-Performance Graph Analysis Retrieved on February 15, 2012
  26. ^ Transaction Processing Performance Council Retrieved on December 25, 2009
  27. ^ The "Top 500" list of High Performance Computing HPC systems Retrieved on July 19, 2016
  28. ^ The Graph 500 Retrieved on February 19, 2012
  29. ^ Resource consumption for billing and performance purposes is measured in units of a million service units MSUs, but the definition of MSU varies from processor to processor in such a fashion as to make MSU's/s useless for comparing processor performance
  30. ^ World's Top Supercomputer Retrieved on December 25, 2009
  31. ^ Cell Broadband Engine Project Aims to Supercharge IBM Mainframe for Virtual Worlds

External linksedit

  • IBM Systems Mainframe Magazine
  • IBM eServer zSeries mainframe servers
  • Mainframe Computer Support Forum since 1998
  • Univac 9400, a mainframe from the 1960s, still in use in a German computer museum
  • Lectures in the History of Computing: Mainframes archived copy from the Internet Archive

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