Abstract: The disk array control system is a fault tolerant controller for arrays of hard disk drives. With the controller as a front end, an array of hard disk drives would appear as a single drive to a host computer system connected to the controller. The controller translates input/output data transfer requests from the host system to input/output data transfer requests for the appropriate drives in the drive array. To minimize latency, translation techniques provide for a minimal number of accesses to the drives in the array. Queued input/output requests are supported, and, to maximize throughput, optimal scheduling techniques are used to optimize resource usage and minimize drive access overheads. Means are provided for detecting module failures, sustaining operation after failure, and replacing faulty modules without interrupting service.