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IBM PC compatible computers are those similar to the original IBM PC, XT, and AT, able to run the same software and support the same expansion cards as those. Such computers used to be referred to as PC clones, or IBM clones. They duplicate almost exactly all the significant features of the PC architecture, facilitated by IBM's choice of commodity hardware components and various manufacturers' ability to reverse engineer the BIOS firmware using a "clean room design" technique. Columbia Data Products built the first clone of the IBM personal computer by a clean room implementation of its BIOS. Early IBM PC compatibles used the same computer bus as the original PC and AT models. The IBM AT compatible bus was later named the Industry Standard Architecture bus by manufacturers of compatible computers. The term "IBM PC compatible" is now a historical description only, since IBM has ended its personal computer sales. Descendants of the IBM PC compatibles comprise the majority of personal computers on the market presently, although interoperability with the bus structure and peripherals of the original PC architecture may be limited or non-existent. ==Origins== IBM decided in 1980 to market a low-cost single-user computer as quickly as possible in response to Apple Computer's success in the burgeoning microcomputer market. On 12 August 1981, the first IBM PC went on sale. There were three operating systems (OS) available for it. The least expensive and most popular was PC DOS made by Microsoft. In a crucial concession, IBM's agreement allowed Microsoft to sell its own version, MS-DOS, for non-IBM computers. The only component of the original PC architecture exclusive to IBM was the BIOS (Basic Input/Output System). IBM at first asked developers to avoid writing software that addressed the computer's hardware directly, and to instead make standard calls to BIOS functions that carried out hardware-dependent operations. This software would run on any machine using MS-DOS or PC-DOS. Software that directly addressed the hardware instead of making standard calls was faster, however; this was particularly relevant to games. Software addressing IBM PC hardware in this way would not run on MS-DOS machines with different hardware. The IBM PC was sold in high enough volumes to justify writing software specifically for it, and this encouraged other manufacturers to produce machines which could use the same programs, expansion cards, and peripherals as the PC. The 808x computer marketplace rapidly excluded all machines which were not hardware- and software-compatible with the PC. The 640 kB barrier on "conventional" system memory available to MS-DOS is a legacy of that period; other non-clone machines, while subject to a limit, could exceed 640 kB. Rumors of "lookalike", compatible computers, created without IBM's approval, began almost immediately after the IBM PC's release. By June 1983 ''PC Magazine'' defined "PC 'clone'" as "a computer (can ) accommodate the user who takes a disk home from an IBM PC, walks across the room, and plugs it into the 'foreign' machine". Because of a shortage of IBM PCs that year, many customers purchased clones instead. Columbia Data Products produced the first computer more or less compatible to the IBM PC standard during June 1982, soon followed by Eagle Computer. Compaq announced its first IBM PC compatible in November 1982, the Compaq Portable. The Compaq was the first sewing machine-sized portable computer that was essentially 100% PC-compatible. The company could not copy the BIOS directly as a result of the court decision in Apple v. Franklin, but it could reverse-engineer the IBM BIOS and then write its own BIOS using clean room design. 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「IBM PC compatible」の詳細全文を読む スポンサード リンク
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