CPU scheduling

CTSS had to keep four, then dozens, of people typing at once without any of them noticing the others. Its scheduler used several queues and a short time slice of about 200 milliseconds: a job that used up its slice was moved down to a lower-priority queue, so short interactive commands stayed responsive while long computations ran in the background. The idea, the multi-level feedback queue, still shapes the schedulers of desktop operating systems.