Gary Kildall

CP/M and the BIOS. Kildall wrote CP/M in 1974 to run a floppy disk drive on an Intel-based machine, and split out the small hardware-specific part into a separate layer he called the BIOS. That meant one operating system, and the programs written for it, could run on hundreds of different makers' computers, the first real software market for microcomputers. His company, Digital Research, missed the IBM PC deal, and MS-DOS borrowed CP/M's design. He died in 1994.