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Mainframe computers (colloquially referred to as "big iron"〔(【引用サイトリンク】title=IBM preps big iron fiesta )〕) 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 computers. Later, the term was used to distinguish high-end commercial machines from less powerful units. Most large-scale computer system architectures were established in the 1960s, but continue to evolve. ==Definition== 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 Linux.〔(【引用サイトリンク】accessdate=September 20, 2011 )〕 In the late 1950s, most mainframes had no explicitly interactive interface. They 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 customer billing, and supported interactive terminals almost exclusively for applications 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 interfaces〔In some cases the interfaces were introduced in the 1960s but their deployment became more common in the 1970s〕 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 interfaces. 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 farms.〔(【引用サイトリンク】publisher=IBM )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mainframe computer」の詳細全文を読む スポンサード リンク
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