Apparatus and method for computer host system and adaptor interrupt reduction including clustered command completion

The number of interrupts are controlled by delaying communication of the interrupt to the host computer or processor according to predetermined rules. This reduces the processing overhead and greatly increases system performance. Application of the inventive structure and method to network servers and RAID disk drive storage arrays is particularly beneficial. In one embodiment, the invention provides structure and method for reducing the number of system interrupts to the host processor to reduce host processor overhead for operation of a computer system having a host processor and a peripheral device coupled to the host processor by a device controller. In another embodiment, the invention provides structure and method for clustering command completion prior to posting completion. System, apparatus, method, and computer program products are described.