Abstract: A pipelined CPU executing instructions of variable length, and referencing memory using various data widths. Macroninstruction pipelining is employed (instead of microinstruction pipelining), with queuing between units of the CPU to allow flexibility in instruction execution times. A wide bandwidth is available for memory access; fetching 64-bit data blocks on each cycle. A hierarchical cache arrangement is used, increasing the likelihood of a cache hit. A writeback cache is used (instead of writethrough) and writeback is allowed to proceed even though other accesses are suppressed due to queues being full. Separate queues are provided for the return data from memory and cache invalidates, yet the order or bus transactions is maintained by a pointer arrangement.

Abstract: A method and apparatus for error detection is disclosed. A data word and its check bits are read from memory, and new check bits are generated form the data word read. A logical operation is performed between the new check bits and the check bits read from memory to generate a syndrome. The syndrome is decoded to detect the presence or absence of an uncorrectable error. If an uncorrectable error is detected, a logical operation is performed between the new check bits and a byte write error code to generate a third set of check bits, which are then written into memory along with the data word.