On Sunday night I got on a subway car. Just after the car pulled away from the station and picked up speed, it can to a hard stop causing some people to fall off their seats. The driver announced that the system had lost 1/3 of its computer.
How do you lose just 1/3 of your computer?
Two guesses:
One: The subway uses three computers for redundancy, as jet fighters and Space Shuttles do. All three computers perform the same calculation and then compare results; if one result disagrees, it is tossed out. If they all disagree, I think the computers average the results and stick with that. The loss of one of the computers may force the train to go into a “safe mode,” and stop as quickly as possible.
Two, the train may have three subsystems on it, for example, one subsystem that controls accelleration and braking; one that tracks other trains on the line and track conditions; and one that controls the lighting and other systems. While this is a very simplified description, the results would be similar to case one above.
Are you sure he didn’t say “One turd of a computer”?
Another wild guess:
The entire system could be run on three computers, the failure of one of which caused the HQ to call for a general shutdown while the problem was located, or alternately caused intermittant service during testing or rebooting. The operator was told by radio the gist of what had happened and passed it along. It doesn’t sound like the stuff of a general public announcement - it sounds like something the driver would say when no one is really telling him what happened.