IBM compatible PC

The concept of an IBM compatible PC reaches back to 1983, to a radical decision made by IBM when it introduced its first personal x86-based personal computer. IBM published the BIOS (Basic Input/Output System) specification for their PC, and then openly encouraged other companies to build components for it, or even create an entirely different incarnation of the hardware which would run the same software. Compaq, around 1985 (check date!), was the first non-IBM company to succeed in creating a completely IBM compatible PC.

To be called IBM compatible, a computer's processor must be x86-based, and all the hardware components must adhere 100% to the BIOS (Basic Input/Output System) specification. Thus, IBM compatibility means hardware compatibility. Beginning in 2006, Apple computer began selling IBM compatible PC's which run the Mac OS X operating system. Such Intel-based Apple computers are also capable of running Microsoft's Windows XP operating system (instead of, or in addition to, Mac OS X). Older Mac computers were not IBM compatible and could not run any version of Microsoft Windows.

IBM's BIOS (Basic Input Output System) specification was key to allowing hardware components manufactured by different companies to interwork. Made available license-free by IBM in 1983, the BIOS specification described exactly how the operating system should interact with its underlying hardware. Any company making a component for an IBM compatible PC was required to implement in firmware the appropriate BIOS calls for that kind of component, thus hiding hardware implementation details from the operating system.