Until about 1990, if you owned a mainframe or a mini, anything that needed chilled air and a raised floor, you knew the vendor field engineer. Because the computer itself, the disk drives, or the tape drives broke and / or required periodic maintenance. pdp 11 was an outlier, as it was highly reliable (and slow as a turtle).
removeable disk packs were always a problem due to head crashes.
my point is, every computer had downtime due to poor reliability, when evaluated against what we have today. and most things were not 'user serviceable', unless your user was highly skilled in electronics, test equipment and digital logic.
In my field, once we moved to SGI's you started to see the salesman a lot more than the FE because the machines were so reliable. And today it is all commodity parts that anyone can cheaply swap-tronix things back to operational.
removeable disk packs were always a problem due to head crashes.
my point is, every computer had downtime due to poor reliability, when evaluated against what we have today. and most things were not 'user serviceable', unless your user was highly skilled in electronics, test equipment and digital logic.
In my field, once we moved to SGI's you started to see the salesman a lot more than the FE because the machines were so reliable. And today it is all commodity parts that anyone can cheaply swap-tronix things back to operational.