I first used a timesharing computer in 1973 in a summer job with the old McDonnell Douglas. It was a Xerox SDS machine. My terminal was an old Teletype 33. This is a fascinating account from one of the early inventors in the field.
“I still don’t understand where all the computer time goes in time-sharing installations, and neither does anyone else.” — John McCarthy, 1983 (Of course, the state of the art has advanced considerably since then; now we don’t even know where the compute time goes in single-user workstations.) [Hack the Planet]