Lars Brinkhoff wrote: I hesitated to post here -- was the CDC 6400 a classic computer? :-) -- but Lars broke the ice. The system ran on a 6400 with Extended Core Storage and Central Exchange Jump (most of the operating system ran on the CPU, counter to normal CDC 6000 practice). The project took place at UC Berkeley between 1968 and 1971 (although hardware acquisition began in 1966). What the university really wanted was simple interactive service (editing, BASIC, remote job submission, etc.) in conjunction with batch jobs running on SCOPE on the main, larger 6400, but what they got was a state-of-the-art research system offering capability-based protection, multiple protection domains per process, and more. Unfortunately, it couldn't support enough concurrent users to be economical. The technical ideas are well-described here: Butler W. Lampson and Howard E. Sturgis. Reflections on an operating system design. Communications of the ACM, 19(5):251-265, January 1976. https://dl.acm.org/doi/abs/10.1145/360051.360074 (open access) The project history is described here: Paul McJones and Dave Redell. History of the CAL Timesharing System. Submitted to: IEEE Annals of the History of Computing. https://www.mcjones.org/CalTSS/paper/cal_tss_history.pdf Through heroic effort, Terry Heidelberg has managed to create an emulation environment and boot the system and run some programs, but it's not ready for prime time! Paul