By the time that the fourth-generation computers were being built, IBM was well established in manufacturing mainframe and minicomputers. IBM's entry into the microcomputer market was relatively late, but turned out to be a defining moment because the IBM PC became a standard. It did so in the sense that other computer manufacturers were keen to ensure that software written for their systems would work on the IBM PC: they wanted to ensure that their software was 'IBM compatible'. This created a bandwagon effect with manufacturers everywhere building IBM-compatible machines. It also gave software developers the incentive they needed and spawned the development of high quality business software such as the spreadsheet Lotus 123 (see later in this chapter). When IBM released the PC, they enlisted the Microsoft Corporation to write the operating system called DOS (Disk Operating System) for the PC and this also became a standard. They also enlisted the microprocessor company Intel to incorporate the 16-bit 8086 microprocessor into their computer. This processor evolved into the 80486, which was replaced by the Pentium processor in the mid-1990s.
The impact of the IBM was such that the PC market became segmented into those that were IBM compatible; and those that were not. The Apple Macintosh computer was developed in 1984, and is the only survivor of that generation that was not IBM compatible. PC computer sales rocketed during the 1990s. Current estimates suggest there are over now 500 million personal computers used in the world.
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