A method and system of executing duplicate copies of a program in lock step. Some illustrative embodiments are a computer system comprising a first processor executing a program, a second processor executing a duplicate copy of the program (the first processor and second processor executing their respective programs in lock step), a logic device coupled to the processors, and a shared device coupled to the processors through the logic device. The first processor presents to the logic device a first operation involving the shared device, and the second processor does not present an operation, or presents an operation that does not match the first operation. The logic device obtains a second operation from the second processor that matches the first operation, and wherein a single operation that matches the first and second operations is presented to the shared device.