A PC clone is a computer that reproduces the behavior of the IBM Personal Computer closely enough to run the same operating system and software, without being built by IBM. The concept matters because it turned IBM’s proprietary product into an open industry standard that IBM did not control.
The technical opening was created by IBM itself. The IBM Personal Computer Technical Reference of August 1981 documented the entire machine and printed the full source listing of the system BIOS. Anyone could buy almost every part of a PC off the shelf, since the processor was Intel’s and the operating system was Microsoft’s. The single component a competitor could not simply copy was the BIOS, because the printed source code in the Technical Reference was IBM’s copyrighted work. Reproducing the BIOS by retyping or paraphrasing it would have been infringement.
The answer was to reimplement the BIOS rather than copy it. A team that had never seen IBM’s code would write fresh firmware that matched the documented, observable behavior of the original, working only from the published interface specification. The surviving ROM artifacts make the result concrete: the Compaq Portable’s system board carries the string “(C) COMPAQ COMPUTER CORP. 1982,” a separate copyright on a separately authored BIOS that nonetheless behaved like IBM’s. Once one company demonstrated this could be done legally, the technique became an industry, and firms like Phoenix Technologies sold compatible BIOS code to anyone who wanted to build a clone.
The long-term effect reshaped the balance of power in computing. As clones drove the price of PC hardware down and turned the machine itself into a commodity, the durable value migrated to the two components every clone still had to license: Microsoft’s operating system and Intel’s processors. IBM had created the standard, but the clone phenomenon ensured that the profits and the platform control would flow to Microsoft and Intel instead.