PC SYSTEM is a term used to refer to a computer system that uses either DOS or UNIX operating systems. DOS, which stands for Disk Operating System, is a single-user, single-tasking operating system developed by Microsoft in the 1980s. UNIX, on the other hand, is a multi-user, multitasking operating system developed by AT&T Bell Labs in the 1970s. Both DOS and UNIX are widely used in the computing industry and have been adapted for use in many different types of computers.