Method for predictive power management for operating a disk drive in a mobile device to optimize power usage

• US 6,892,313 B1
• Filed: 06/21/2001
• Issued: 05/10/2005
• Est. Priority Date: 06/21/2001
• Status: Active Grant

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Codilian, Raffi, Sareen, Anil
• Primary Examiner(s): Browne, Lynne H.
• Assistant Examiner(s): YANCHUS III, PAUL B
• Application Number:
  US09/887,583
• Time in Patent Office: 1,419 Days
• Field of Search: 713/320, 713/322, 713/323, 713/324, 713/300, 360/69, 360/73, 360/75, 365/226, 365/227, 365/229
• US Class Current: 713/323
• CPC Class Codes: G06F 1/3203 Power management, i.e. event-based initiation of a power-saving mode
• CPC Class Codes: G06F 1/3268 Power saving in hard disk drive
• CPC Class Codes: G06F 3/0625 Power saving in storage systems
• CPC Class Codes: G06F 3/0653 Monitoring storage devices or systems
• CPC Class Codes: G06F 3/0674 Disk device
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

The invention may be embodied in a method for operating a disk drive in a mobile device to optimize power usage. The mobile device may be a hand held computing device such as a personal digital assistant (PDA) or a mobile terminal such as a cellular telephone. Immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power. A transition from the second operating mode to the first operating mode consumes a transition quantity of power. A predictive technique tracks a user'"'"'s usage pattern and adapts an operating mode transition time based on the usage pattern.

Claims

1. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the method comprising the steps of:

setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold;

setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

2. A method for operating a disk drive as defined in claim 1, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

3. A method for operating a disk drive as defined in claim 2, wherein the second time period threshold is less than the exchange time interval.

4. A method for operating a disk drive as defined in claim 1, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the second time period threshold.

5. A method for operating a disk drive as defined in claim 1, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals are measured using the most recent disk access commands.

6. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the method comprising the steps of:

setting first and second time period thresholds, the first time period threshold being less than the second time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, and the second time period threshold is about 66% of the exchange time interval;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold;

setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

7. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the method comprising the steps of:

setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold;

setting the delay time interval to be equal to about the second time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

8. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the method comprising the steps of:

setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold;

setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold;

setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

9. A method for operating a disk drive as defined in claim 8, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

10. A method for operating a disk drive as defined in claim 9, wherein the third time period threshold is less than the exchange time interval.

11. A method for operating a disk drive as defined in claim 8, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals are measured using the most recent disk access commands.

12. A method for operating a disk drive as defined in claim 8, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the third time period threshold.

13. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the method comprising the steps of:

setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, the second time period threshold is about 33% of the exchange time period, and the third time period threshold is about 66% of the exchange time interval;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold;

setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold;

setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

14. A method for operating a disk drive in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the method comprising the steps of:

setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

setting the delay time interval to be equal to about the first time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold;

setting the delay time interval to be equal to about the second time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold;

setting the delay time interval to be equal to about the third time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

15. A mobile device having a disk drive wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

16. A mobile device having a disk drive as defined in claim 15, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

17. A mobile device having a disk drive as defined in claim 16, wherein the second time period threshold is less than the exchange time interval.

18. A mobile device having a disk drive as defined in claim 15, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals used by the means for setting the delay time interval are measured using the most recent disk access commands.

19. A mobile device having a disk drive as defined in claim 15, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the second time period threshold.

20. A mobile device having a disk drive wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, and wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, and the second time period threshold is about 66% of the exchange time interval;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

21. A mobile device having a disk drive wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

22. A mobile device having a disk drive wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

23. A mobile device having a disk drive as defined in claim 22, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

24. A mobile device having a disk drive as defined in claim 23, wherein the third time period threshold is less than the exchange time interval.

25. A mobile device having a disk drive as defined in claim 22, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals used by the means for setting the delay time interval are measured using the most recent disk access commands.

26. A mobile device having a disk drive as defined in claim 22, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the third time period threshold.

27. A mobile device having a disk drive wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, and wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, the second time period threshold is about 33% of the exchange time period, and the third time period threshold is about 66% of the exchange time interval;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

28. A mobile device having a disk drive wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

29. A disk drive for use in a mobile device wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

30. A disk drive as defined in claim 29, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

31. A disk drive as defined in claim 30, wherein the second time period threshold is less than the exchange time interval.

32. A disk drive as defined in claim 29, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals used by the means for setting the delay time interval are measured using the most recent disk access commands.

33. A disk drive as defined in claim 29, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the second time period threshold.

34. A disk drive wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, and the second time period threshold is about 66% of the exchange time interval;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

35. A disk drive wherein, immediately after responding to a disk access command from the mobile device, the disk drive is in a first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first and second time period thresholds, the first time period threshold being less than the second time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the second time period threshold, and setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

36. A disk drive for use in a mobile device wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

37. A disk drive as defined in claim 36, wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power.

38. A disk drive as defined in claim 37, wherein the third time period threshold is less than the exchange time interval.

39. A disk drive as defined in claim 36, wherein the demand time intervals comprising the predetermined number of the plurality of demand time intervals used by the means for setting the delay time interval are measured using the most recent disk access commands.

40. A disk drive as defined in claim 36, wherein the majority for setting the demand time interval to be equal to about the first time period threshold includes at least one demand time interval that falls within the time period greater than the third time period threshold.

41. A disk drive wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, and wherein transitioning from the second operating mode to the first operating mode consumes a transition quantity of power, and an exchange time interval is defined as a time period during which power consumed by operating in the first power operating mode is about equal to the transition quantity of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold, wherein the first time period threshold is about 0.3% of the exchange time interval, the second time period threshold is about 33% of the exchange time period, and the third time period threshold is about 66% of the exchange time interval;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if a majority of a predetermined number of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.

42. A disk drive wherein, immediately after responding to a disk access command, the disk drive is in first operating mode that consumes a relatively high level of power and may transition to a second operating mode that consumes a relatively low level of power, the disk drive comprising:

means for setting first, second and third time period thresholds, the first time period threshold being less than the second time period threshold and the second time period threshold being less than the third time period threshold;

means for providing an adjustable delay time interval that is set to correspond to one of the time period thresholds, the delay time interval being the time interval for waiting after an end of a response to a disk access command before transitioning from the first operating mode to the second operating mode;

means for measuring a demand time interval for each of a plurality of disk access commands, wherein each demand time interval is defined as a time period between an end of a response to a last disk access command and an arrival of a next disk access command;

means for setting the delay time interval to be equal to about the first time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period less than the first time period threshold or a time period greater than the third time period threshold, setting the delay time interval to be equal to about the second time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the first time period threshold and the second time period threshold, and setting the delay time interval to be equal to about the third time period threshold if 4 of 7 of the plurality of demand time intervals falls within a time period between the second time period threshold and the third time period threshold; and

means for transitioning the disk drive from the first operating mode to the second operating mode after expiration of the delay time interval.