I'm in same era as you
@ShowMeTwice, back from when there UPSI switches, and punch cards. I was at Motorola and being a federal supplier, arpanet was king. We could telnet of FTP or TFTP to other contractors (mainly Boeing) or universities. My first email address was
be548@email.mot.com. Usenet was great.
We had one IBM datacenter that was 12K square feet. You forgot to mention 'chillers'. There was so much heat generated, there was a jug (can't remember if it was anti-freeze or water) beside some cabinets.
In our HP dataceneter we had those replaceable hard drives. 4@5Mb platters that were interchangable.
Because they were the 68000 creator I got access to all their new chips like their early 8800 chips and UNIX. We had the source code to UNIX System V before the split.
We've come a long way.