The term PC Operating System refers to the software that is installed on a computer to manage its hardware and software resources. Three of the most popular PC Operating Systems are Linux, DOS, and UNIX. Linux is an open-source operating system that is based on the Linux kernel and is used in many different types of computers. DOS stands for Disk Operating System and is a single-user, single-tasking operating system developed by Microsoft. UNIX is a multi-user, multitasking operating system developed by AT&T Bell Laboratories.