Cray XMP/1 System Programmer Reference Manual (1987) [pdf]

I'm always fascinated by the supercomputers of the past. Sometimes we forget that the literally fastest computers in the world 40 years ago have the performance of a $20 NanoPi Neo (four cores, 200 MFLOPS/core, 345 or so milliamps at 5 volts instead of 345 kilowatts).

What makes me sad is that there was so much work to make software that took advantage of those awesome systems, but most of that software is gone now. It'd be wonderful if we could try out and learn from supercomputing software from the past.