Space-efficient expected access time algorithm for hard disk drive command queue ordering

A computer program product for hard disk drive command queue ordering in a disk drive including a processor unit, said computer program product including a plurality of computer executable instructions stored on a computer readable medium, wherein said instructions, when executed by said processor unit, cause the processor unit to perform the steps of:

• for each command in said hard disk drive command queue, calculating an expected access time including a probability of success calculation;
• for an estimated seek time of less than a time for one full revolution, said probability of success calculation including a calculation of a probability of a miss multiplied by a time of one extra revolution, and for an estimated seek time of greater than a time for one full revolution, said probability of success calculation including a calculation of a probability of a make multiplied by a time of one extra revolution;
• identifying a command in said hard disk drive command queue having a minimum calculated expected access time;
• and
• executing said identified command having a minimum calculated expected access time.

Apparatus for hard disk drive command queue ordering comprising:

• a processor;
• a seek classification table coupled to said processor;
• said seek classification table including a plurality of cylinder groups, each cylinder group including a plurality of arrival bands and said seek classification table storing both make and miss counters for each entry in said arrival band versus cylinder group;
• said processor for each command in said hard disk drive command queue, for calculating an expected access time including a probability of success calculation;
• said probability of success calculation utilizing said make and miss counters;
• said processor for identifying a command in said hard disk drive command queue having a minimum calculated expected access time;
• and
• said processor for executing said identified command having a minimum calculated expected access time.