Fault-tolerant memory design in the IBM application system/400

Some of the fault-tolerant features of the IBM AS/400 main storage subsystem are described, with particular attention to the error-correcting code for the 4-bit-per-chip memory array. Single 4-bit symbol errors are automatically corrected, and double symbol errors are detected and corrected with additional machine cycles. The procedure, which is implemented in hardware, is described. The AS/400 storage model and management and the memory maintenance strategy are described. >