Disk drive command queuing method using two memory devices for storing

Abstract

Automatic disk drive command reception by an interface ASIC circuit from a host without firmware intervention lowers host-disk bus overhead. Separate command manipulation is used to build a command queue subject to performance enhancing features. The interface ASIC manages a FIFO and LIFO data structure in DRAM memory and immediately places incoming non-head-of-queue commands in the FIFO and head-of-queue commands in the LIFO. Collecting commands from DRAM memory and placing such commands into an SRAM command queue subject to performance enhancing features occurs independently of command reception. As a result, host-disk bus utilization is increased and the command storage capacity of the disk drive is not limited by the size of the SRAM command queue. Performance enhancing features still apply to a substantial number of queued commands, yet the number of commands which may be readily accepted from a host computer and held by the disk drive remains high.