The term 'EARLY PC SYSTEM' can be summarized as the MS-DOS operating system, which was released in 1981 by Microsoft. It was the first operating system to be widely used on personal computers, and it quickly became the industry standard for PC systems. MS-DOS was a command-line based operating system, meaning that users had to type commands in order to use the system. Despite its limitations, MS-DOS was an important milestone in the development of personal computing.