Before Linux OS

–        In 80’s, Microsoft’s DOS was the dominated OS for PC

    – single-user, single-process system

–     Apple MAC is better, but expensive

–     UNIX is much better, but much much expensive. Only for                    minicomputer for commercial applications

–     People was looking for a UNIX based system, which is cheaper           and can run on PC

–     Both DOS, MAC and UNIX are proprietary, i.e., the source code of           their kernel is protected

–        No modification is possible without paying high license fees

Before Linux OS