[stinos]

If one of them fails, the rover could use the other as a backup

Any idea how that works practically? I mean, there are two boards and one set of peripherals. Is there like an external controller which constantly checks if board A is doing fine, and if not, somehow reroutes all peripheral communication to board B?

[avar]

The NASA website seems to imply that it's done manually: http://mars.jpl.nasa.gov/msl/mission/rover/brains/

Presumably there's some basic functions in the radio stack they use where they can trigger operations like shutdown, startup, reboot, switch boards etc.

[gsnedders]

NASA normally has pretty low-level stuff. To the point of being able to do full firmware updates — though obviously that's something they don't want to risk ordinarily.