1. A computer system comprising: a first processor that executes a program, wherein the program of the first processor has a program counter and a graduated instruction counter; a second processor that executes a duplicate copy of the program in lock-step with the first processor, wherein the program of the second processor has a program counter and a graduated instruction counter; wherein after receipt of a duplicate copy of an interrupt request by each processor, the first processor determines the execution point in its program relative to the execution point of the duplicate copy of the program by comparing the program counter and graduated instruction counter of the first processor with the program counter and graduated instruction counter of the second processor.