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. To widespread industry amazement, IBM published the behavioral specifications of their PC and 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.

The key to allowing hardware components manufactured by different companies to interwork smoothly was the BIOS (Basic Input Output System) specification. This specification, made available license-free by IBM in 1983, described exactly how the operating system (made by Microsoft) would interact with its underlying hardware. Any company making a component for an IBM compatible PC was required to implement in firmware the BIOS calls, this hiding hardware implementation details from the operating system.