IBM PC compatible computers are those similar to the original
IBM PC,
XT, and
AT, able to run the same software and support the same
expansion cards as those. Such computers used to be referred to as
PC clones, or
IBM clones. They duplicate almost exactly all the significant features of the PC architecture, facilitated by IBM's choice of commodity hardware components and various manufacturers' ability to
reverse engineer the
BIOS firmware using a "
clean room design" technique.
Columbia Data Products built the first clone of the IBM
personal computer by a clean room implementation of its BIOS.