At one time during system checkout we had a very elusive problem which we couldn’t pin down. In looking over the programs, we realized that the symptoms we were seeing could occur if an unconditional jump instruction failed to jump. We therefore asked CDC whether they had any indication that that instruction occasionally misbehaved. The reply was, “Oh, no. That’s one of the more reliable instructions,” This was our first indication that commands could be ordered by reliability.Montgomery Phister, Jr., 1989
I'm just glad someone interviewed the engineers back then, to preserve those stories for us today.