n.

A large powerful computer, often serving many connected terminals and usually used by large complex organizations.

mainframe

A large, powerful computer system. A typical mainframe computer will fill a good-sized room.

A state-of-the-art computer for mission critical tasks. In the "ancient" mid-1960s, all computers were mainframes, since the term referred to the main CPU cabinet. Today, it refers to a class of ultra-reliable medium and large-scale servers designed for enterprise-class and carrier-class operations.

The first mainframe vendors were Burroughs, Control Data, GE, Honeywell, IBM, NCR, RCA and Univac, otherwise known as "IBM and the Seven Dwarfs." After GE and RCA's computer divisions were absorbed by Honeywell and Univac respectively, the mainframers were known as "IBM and the BUNCH."

The Vendors

For decades, IBM has been the dominant vendor in the mainframe business. Although many tried to compete by offering IBM-compatible mainframes, only Amdahl (Fujitsu) has remained as a competitor in this arena (see IBM-compatible mainframe). Unisys, Sun and others also make mainframe-class machines that typically run under a version of Unix or Linux.

There Is a Difference

One might wonder why mainframes cost a million dollars or more when the raw gigahertz (GHz) rating of their CPUs is not any higher than a PC costing 1,000 times less. Quite often in fact, the ratings are lower. Here are the reasons.

Lots of Processors, Memory and Channels

Mainframes support symmetric multiprocessing (SMP) with several dozen central processors in one system. They are highly scalable. CPUs can be added to a system, and systems can be added in clusters. Built with multiple ports into high-speed caches and main memory, a mainframe can address thousands of gigabytes of RAM. They connect to high-speed disk subsystems that can hold terabytes of data.

Enormous Throughput

A mainframe provides exceptional throughput by offloading its input/output processing to a peripheral channel, which is a computer itself. Mainframes can support hundreds of channels, and additional processors may act as I/O traffic cops that handle exceptions (channel busy, channel failure, etc.).

All these subsystems handle the transaction overhead, freeing the CPU to do real "data processing" such as computing balances in customer records and subtracting amounts from inventories, the purpose of the computer in the first place.

Super Reliable

Mainframe operating systems are generally rock solid because a lot of circuitry is designed to detect and correct errors. Every subsystem may be continuously monitored for potential failure, in some cases even triggering a list of parts to be replaced at the next scheduled maintenance. As a result, mainframes are incredibly reliable with mean time between failure (MTBF) up to 20 years!

Here to Stay

Once upon a time, mainframes meant "complicated" and required the most programming and operations expertise. Today, networks of desktop clients and servers are just as complex, if not more so. Large enterprises have their hands full supporting thousands of PCs along with Windows, Unix and Linux and maybe some NetWare and Macintosh for good measure.

With trillions of dollars worth of mainframe applications in place, mainframes may hang around for quite a while. Some even predict they are the wave of the future! See midrange computer.

Mainframe System

UNIVAC Mainframe

Mainframes have provided the computing power for major corporations for more than 40 years. Sperry Rand (Univac), IBM, GE, RCA, NCR, Burroughs, Honeywell and Control Data were the first companies that made mainframes in the U.S. This picture was taken in the mid-1970s.

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Main computer or central processing unit in what is typically a full-size computer system. Computers have made it possible to handle large amounts of data quickly and accurately. The major drawbacks to the large mainframes are that they generally require climate-controlled rooms and a technically adept staff to run, maintain, and program them. Computers are omnipresent in marketing, used to maintain and merge/purge lists; to analyze consumer characteristics, promotion response, and product sales information, to fulfill orders, to compose type; and so forth. See also microcomputer; minicomputer.

Large computer that may support 100-500 users at one time. Typically, mainframes have a word length of 64 bits and are significantly faster and have greater capacity than the minicomputer and the microcomputer. Mainframes are recommended when vast amounts of data must be processed.

Term originally referring to the cabinet containing the central processor unit or ‘main frame’ of a room-filling Stone Age batch machine. After the emergence of smaller minicomputer designs in the early 1970s, the traditional big iron machines were described as ‘mainframe computers’ and eventually just as mainframes. The term carries the connotation of a machine designed for batch rather than interactive use, though possibly with an interactive timesharing operating system retrofitted onto it; it is especially used of machines built by IBM, Unisys, and the other great dinosaurs surviving from computing's Stone Age.

It has been common wisdom among hackers since the late 1980s that the mainframe architectural tradition is essentially dead (outside of the tiny market for number-crunching supercomputers having been swamped by the recent huge advances in IC technology and low-cost personal computing. The wave of failures, takeovers, and mergers among traditional mainframe makers in the early 1990s bore this out. The biggest mainframer of all, IBM, was compelled to re-invent itself as a huge systems-consulting house. (See dinosaurs mating and killer micro).

However, in yet another instance of the cycle of reincarnation, the port of Linux to the IBM S/390 architecture in 1999 — assisted by IBM — produced a resurgence of interest in mainframe computing as a way of providing huge quantities of easily maintainable, reliable virtual Linux servers, saving IBM's mainframe division from almost certain extinction.

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For more information on mainframe, visit Britannica.com.

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - central computer

Nederlands (Dutch)
mainframe, zeer grote snelle computer, computerkast etc.

Français (French)
n. - ordinateur central

Deutsch (German)
n. - (Comp.) Großrechner

Ελληνική (Greek)
n. - (τεχνολ.) κεντρική μονάδα Η/Υ, μεγάλος υπολογιστής

Italiano (Italian)
unità di elaborazione centrale

Português (Portuguese)
n. - computador de grande porte (m) (Comp.)

Русский (Russian)
главный компьютер, центральный процессор

Español (Spanish)
n. - unidad central, computadora/ordenador principal

Svenska (Swedish)
n. - stordator

中文（简体） (Chinese (Simplified))
主机

中文（繁體） (Chinese (Traditional))
n. - 主機

한국어 (Korean)
n. - 컴퓨터 본체

日本語 (Japanese)
n. - メインフレーム, 大型コンピューター

العربيه (Arabic)
‏(الاسم) الحاسبه الإلكترونيه الكبيرة‏

עברית (Hebrew)
n. - ‮מחשב גדול/עיבוד מרכזי‬

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