Also short lived as CMOS got faster.. The difference is that Cray was pushing tech harder than most and enjoyed the unique position of faster than most by alot could justify the cost and complexity. To do that they had to be smaller (the old 1ns/ft problem) and that was a heat vs volume issue. Refigeration was the only way out. They would revisit that again with the XMP. However over time the same scene tended to play out. Those that pushed and resorted to exotic cooling would be pushed out. Also those exoticly cooled machines tended to not find a second market making them scarce faster. Likely not. If there was it would be a really bad scene. I bet any shutdown for more than minutes would have been viewed quite severely. My view of that period was large systems ran 24/7 and all maintenence was to be closely scheduled. I bet the CEs were also checking the loop and maybe running a pressure hold test on occasion to assure integrity. But the designers had to have paid close attention to things like assembly repair, vibration and what not to insure it worked as expected planned. Remins me of the mainframe mini joke I'd heard years ago. Minis have power switches, mainframes have BIG RED BUTTONS (emergency power off). Allison