Abstract: A clock switching circuit switches between clock signals generated by a local clock unit and those generated by a-system clock unit when disabling, and then subsequently enabling, the system clock unit. The clock switching circuit includes a plurality-of switching circuits that are arranged and configured to switch between the system and local clock units so as to provide a substantially uninterrupted stream of clock signals to selected components of a fault-tolerant computer system. This arrangement ensures that information stored on the selected components is not lost during disablement of the system clock unit.