Command stack management in a disk drive

An intelligent disk drive is described which includes means for prioritizing execution of command by maintaining an associated priority with each command in a pending command list and executing the highest priority commands first. The command structure according to the invention includes a field in which the host specifies the priority of the command. One embodiment uses a plurality of stacks which are used to sort the command according to priority. Another embodiment uses a list structure. In an alternative embodiment the drive has means for ensuring that designated data written to the disk is not subject to fragmentation. The disk drive embodiments described above can be implemented in an intelligent disk drive with distributed processing capability.