Hypervisor-based fault tolerance

Protocols to implement a fault-tolerant computing system are described. These protocols augment the hypervisor of a virtttalmachine manager and coordinate a primary virtual machine with its backup. The result is a fault-tolerant computing system. No modification to hardware, operating system, or application programs is required. A prototype system was constructed for HP's PA-RISC instruction-set architecture. The prototype was able to run programs about a factor of 2 slower than a bare machine would.