Talisman is a simulator that models the execution semantics and timing of a multicomputer. Talisman is unique in combining high semantic accuracy, high timing accuracy, portability, and good performance. This good performance allows users to run significant programs on large simulated multicomputers. The combination of high accuracy and good performance yields an ideal tool for evaluating architectural trade-offs. Talisman models the semantics of virtual memory, a circuit-switched internode interconnect, I/O devices, and instruction execution in both user and supervisor modes. It also models the timing of processor pipelines, caches, local memory buses, and a circuit-switched interconnect. Talisman executes the same program binary images as a hardware prototype at a cost of about 100 host instructions per simulated instruction. On a suite of accuracy benchmarks run on the hardware and the simulator, Talisman and the prototype differ in reported running times by only a few percent.