I apologize if this has already been posted.
For safety critical system design folks:
Spaceflight Now | STS-135 Shuttle Report | Astronauts restart computer; Obama to call Atlantis today
From the article: (bolding mine)
"Well, it [flight computer] actually failed last night, I think it was about an hour and a half after we fell asleep the alarm went off," Ferguson told CBS Radio in an orbital interview. "I think we all looked at each other, had that bright-eyed, sort of bushy-tailed look, and raced up to the flight deck. The folks on the ground did a nice job helping us get through that. We brought up another GPC to help out with the functions (GPC-)4 was performing. We got it, hopefully, back up and running this morning so it's hanging in there and we're confident it's going to work for entry for us."