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 tends to me hardware compatibility, rather than software. For example, in 2006, Apple computer for the first time began selling versions of an IBM personal computer, one which runs Apple's MAC OS X operating system but is also capable of running Windows instead, or in addition to, MAC OS X. Before 2006, all Apple personal computers were not IBM compatible because they ran on a non-x86 hardware base.

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.