IBM compatible PC

The concept of an IBM compatible PC reaches back to 1981, to a radical decision made by IBM when it introduced its first personal computer (x86-based). 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 1983 , 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.

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.

Further reading

• James Chposky, Ted Leonsis, Blue Magic: The People, Power and Politics Behind the IBM Personal Computer, Facts on File, New York, 1988 (ISBN 0-8160-1391-8) A very readable and carefully researched history of the early days of the original IBM PC, based on extensive interviews with many members of the original team which created it.