The timesharing system TSS-8 was developed by Don Witcraft and John Everett at DEC, starting in late 1967, and with the first beta sites up and running in the fall of 1968. This was based on a protection architecture proposed by Adrian Van Der Goor, a grad student of Gordon Bell’s at Carnegie-Mellon.

It requires a minimum of 12K words of memory and a swapping device; on a 24K word machine, it could give good support for 17 users. It was the standard operating system on the EduSystem 50 which was sold to many
small colleges and large public school systems. The first installation was at Lexington High School in Massachusetts, and the second was at Northern Arizona University.

Each user gets a virtual 4K PDP-8; many of the utilities users ran on these virtual machines were only slightly modified versions of utilities from the Disk Monitor System or paper-tape environments. Internally, TSS8 consists of RMON, the resident monitor, DMON, the disk monitor (file system), and KMON, the keyboard monitor (command shell). BASIC was well supported, while restricted (4K) versions of FORTRAN D and Algol were available.