DESKTOP SYSTEMS:
Personal compuers PCs appeared in the 1970's. During this first decades, the CPUs in PCs lacked the features needed to protect an operating system from user programs. PC operating system therefore were neither multi user non multi tasking.
These system include PCs running microsoft windows and the apple macintosh. The MS-DOS operating system from microsoft has been superseded by multiple flavors of microsoft windows and IBM has upgraded MS-DOS to the OS/2 multi tasking system. The apple macintosh operating system has been ported to more advanced hardware and now includes new features, such as virtual memory and multi tasking operating.