Abstract: An Externally Specified Index (ESI) peripheral simulator portion of an ESI eripheral simulation system allows a plurality of parallel word input/output (I/O) channels of a tactical computer to communicate with each other as if real peripheral equipment were attached thereto. A simulation computer having a similar plurality of parallel word I/O channels is operatively connected to the ESI peripheral simulator such that it converts the interface signals of the simulation computer to be compatible with the interface signals of the tactical computer. Accordingly, the function of the ESI peripheral simulator is to simulate tactical peripherals. It accomplishes the foregoing function by using information transferred to it by the simulation computer.