In designing a self-checking processor, it is essential to recognize the types of failures that are most probable. Matching the checking techniques with the type of faults that are expected to occur should yield the best result with the least amount of hardware. The microprogram control will consist of integrated circuits: large-scale integration (LSI) for the memory and small-scale integration (SSI) for the associated control logic. Because of the density of chips on a plug-in package and the physical proximity of the devices on an integrated circuit, multiple faults within a single circuit are highly probable. The types of faults within a circuit have been analyzed and found to be of the type which would tend to affect the bits in a unidirectional manner. Also the failed bits would probably be adjacent rather than randomly dispersed throughout-the microprogram store word.