The PDP-10 family ran a few operating systems in its life, some of which had better or worse user interfaces, but one of the things the all had in common was a

The PDP-10 family ran a few operating systems in its life, some of which had better or worse user interfaces, but one of the things the all had in common was a focus on interactive use as opposed to batch operation or even block-mode terminals. Interactive use means each concurrent user represents more system load compared to the alternatives.