Yes, but you have to compare the complete state of each computer for this to work, including every bit of memory & cache. You can't have much RAM if you're plan

Yes, but you have to compare the complete state of each computer for this to work, including every bit of memory & cache. You can't have much RAM if you're planning to compare them in a few milliseconds. If you try to do this without comparing the whole state, and only comparing the outputs of some control algorithm between the computers, one of them could have some internal state corrupted and remain unnoticed for a long time, long enough for other corruptions to happen on the other computers, and then you have no straightforward way to figure out which one to trust and which to reset.