Mainframe computer

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Mainframe computer From Wikipedia, the free encyclopedia Jump to: navigation, search This article or section does not cite its references or sources. Please help improve this article by introducing appropriate citations. (help, get involved!) This article has been tagged since October 2006. For other uses, see Mainframe. A Honeywell-Bull DPS 7 mainframe, circa 1990.Mainframes (often colloquially referred to as Big Iron) are computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry/consumer statistics, ERP, and financial transaction processing. The term originated during the early years of computing and referred to the large mechanical assembly that held the central processor and input/output complex. Later the term was used to distinguish high-end commercial machines from less powerful units which were often contained in smaller packages. Today, this term refers primarily to IBM System z9 mainframes, the lineal descendants of the System/360, but it is also used for the lineal descendents of the Burroughs large systems and the UNIVAC 1100/2200 series mainframes. Contents[hide] 1 Description 2 Characteristics 3 Market 4 History 5 Mainframes vs. supercomputers 6 Statistics 7 Speed and performance 8 See also 9 References 10 External links [edit] Description Modern mainframe computers have abilities not so much defined by their single task computational speed (Gbops or Gigahertz) as by their redundant internal engineering and resulting high reliability and security, and strict backward compatibility for older software. These machines often run for years without interruption, with repairs taking place during normal operation. They are defined by high availability, one of the main reasons for their longevity, as they are used in applications where downtime would be costly or catastrophic. The term Reliability, Availability and Serviceability (RAS) is a defining characteristic of mainframe computers. In the 1960s, most mainframes had no user interface per se. They accepted sets of punch cards and operated solely in batch mode to support back office functions. Teletype devices were also common, especially for system operators. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, supporting hundreds or thousands of users simultaneously along with batch processing. Users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. Many mainframes supported graphical terminals (and terminal emulation) by the 1980s (if not earlier). In 1990, an IBM mainframe became the first Web server located anywhere outside Switzerland's CERN organization (see: History of the World Wide Web), and nowadays most mainframes have partially or entirely phased out user terminal access. Historically mainframes acquired their name in part because of their substantial size and requirements for specialized HVAC and electrical power. Those requirements ended by the mid-1990s, with CMOS mainframe designs replacing the older bipolar technology. An IBM z890 mainframe, circa 2004. This model is 1.94 meters tall and occupies 1.24 square meters of floorspace. [edit] Characteristics Nearly all mainframes have the ability to run (or "host") multiple operating systems and thereby operate not as a single computer but as a number of virtual machines. In this role, a single mainframe can replace dozens or even hundreds of smaller servers, reducing management and administrative costs while providing greatly improved scalability and reliability. Mainframes can add system capacity nondisruptively and granularly. Modern mainframes, notably the IBM zSeries and System z9 servers, offer three levels of virtualization: logical partitions (LPARs, via the PR/SM facility), virtual machines (via the z/VM operating system), and through its operating systems (notably z/OS with its key-protected address spaces and sophisticated goal-oriented workload scheduling, but also Linux and Java). 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. Some argue that the modern mainframe is not cost-effective. Sun Microsystems, Hewlett-Packard, and Dell unsurprisingly take that view at least at times, and so do some independent analysts. However, the general consensus (held by Gartner and other independent analysts) is that the modern mainframe often has unique value and superior cost-effectiveness, especially for large scale enterprise computing. In fact, Hewlett-Packard also continues to manufacture its own mainframe, the NonStop system originally created by Tandem. Logical partitioning is now found in many high-end UNIX-based servers, and many vendors are promoting virtualization technologies, in many ways validating the mainframe's design accomplishments. Mainframes also have unique execution integrity characteristics for fault tolerant computing. System z9 servers execute each instruction twice, compare results, and shift workloads "in flight" to functioning processors, including spares, without any impact to applications or users. This feature, also found in HP's NonStop systems, is known as lock-stepping, because both processors take their "steps" (i.e. instructions) together. Not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing. [edit] Market As of early 2006, IBM mainframes dominate the mainframe market at well over 90% market share, however IBM is not the only vendor. Unisys manufactures ClearPath mainframes, based on earlier Sperry and Burroughs product lines, and a recent survey suggests its customers are loyal. Fujitsu's Nova systems are rebranded Unisys ES7000's. Hitachi co-developed the zSeries 800 with IBM to share expenses. Hewlett-Packard sells its unique NonStop systems, which it acquired with Tandem Computers, and Groupe Bull's DPS mainframes are available in Europe. Unisys and HP increasingly rely on commodity Intel CPUs rather than custom processors in order to reduce development expenses, while IBM has its own large research and development organization to introduce new, homegrown mainframe technologies. [edit] History Several manufacturers produced mainframe computers from the late 1950s through the 1970s. At this time they were known as "IBM and the Seven Dwarfs": Burroughs, Control Data, General Electric, Honeywell, NCR, RCA, and UNIVAC. 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/z9 mainframes which, along with the then Burroughs and now Unisys MCP-based mainframes, are among the few mainframe architectures still extant that date from this early period. That said, while they can still run 24-bit System/360 code, the 64-bit zSeries and System z9 CMOS servers have almost nothing physically in common with the older systems. The larger of the latter IBM competitors were also often referred to as "The BUNCH" from their initials (Burroughs, UNIVAC, NCR, CDC, Honeywell). Notable manufacturers outside the USA were Siemens and Telefunken in Germany, ICL in the United Kingdom, and Fujitsu, Hitachi, and NEC in Japan. The Soviet Union and Warsaw Pact countries manufactured close copies of IBM mainframes during the Cold War. Shrinking demand and tough competition caused a shakeout in the market in the early 1980s — RCA sold out to UNIVAC and GE also left; Honeywell was bought out by Bull; UNIVAC became a division of Sperry) which later merged with Burroughs to form Unisys Corporation in 1986. In 1991, AT&T 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 consensus among industry analysts that the mainframe was a dying market as mainframe platforms were increasingly replaced by personal computer networks. That trend started to turn around in the late 1990s as corporations found new uses for their existing mainframes. 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. Another factor currently increasing mainframe use is the development of the Linux operating system, which can run on many mainframe systems, typically in virtual machines. Linux allows users to take advantage of open source software combined with mainframe hardware RAS. Rapid expansion and development in emerging markets, particularly China, is also spurring major mainframe investments to solve exceptionally difficult computing problems, e.g. providing unified, extremely high volume online transaction processing databases for 1 billion consumers across multiple industries (banking, insurance, credit reporting, government services, etc.) [edit] Mainframes vs. supercomputers The distinction between supercomputers and mainframes is not a hard and fast one, but supercomputers generally focus on problems which are limited by calculation speed while mainframes focus on problems which are limited by input/output and reliability. The differences and similarities include:Both types of systems offer parallel processing. Supercomputers typically expose it to