Actually, while 60s era mainframes did require significant maintenance by the time the late 70s came around up-time was much better. I still have a late 70s mini-computer that I keep around for laughs that routinely gets about a year and a half between reboots, running 11 users and multi-tasking for each user. As for features that come and go, the IBM 7030 had instruction pipe-lining and look-ahead (what Intel calls hyper-threading) way back in the 60s. In fact it could have as many as 11 instructions in the pipeline at any time. (Though 4 was typical) That went away in the era of the microprocessor, not because it was a bad idea, but because it wasn't possible to implement in early primitive Intel processors. Only after technology caught up again did it reappear as hyper-threading.