motd.co: Phoenix Technologies: Cloning the IBM PC BIOS
Phoenix Technologies: Cloning the IBM PC BIOS
With the success of the IBM PC in 1983, Phoenix decided to provide an IBM PC compatible ROM BIOS to the PC market. A licensable ROM BIOS would allow clone PC manufacturers to run the same applications, and even the MS-DOS that was being used by IBM. However, to do this Phoenix needed a strategy for defense against IBM copyright infringement lawsuits. IBM would claim that the Phoenix programmers had copied parts of the IBM BIOS code published by IBM in its Technical Reference manuals. Due to the nature of low-level programming two well-written pieces of code that perform the same function there will inevitably be some degree of similarity. As such it would be impossible for Phoenix to defend itself on the grounds that no part of its BIOS matched IBM’s. Phoenix developed a “clean room” technique that isolated the engineers who had been contaminated by reading the IBM source listings in the IBM Technical Reference Manuals. The contaminated engineers wrote specifications for the BIOS APIs and provided the specifications to “clean” engineers who had not been exposed to IBM BIOS source code. Those “clean” engineers developed code from scratch to mimic the BIOS APIs. This technique provided Phoenix with a defensibly non-infringing IBM PC-compatible ROM BIOS. Because the programmers who wrote the Phoenix code had never read IBM’s reference manuals, nothing they wrote could have been copied from IBM’s code, no matter how closely the two matched. The first Phoenix PC ROM BIOS was introduced in May, 1984, and helped fuel the growth in the PC industry.