Disk drive booting from volatile semiconductor memory when exiting power save mode

1. A disk drive comprising:

a disk;

a head actuated over the disk;

a first volatile semiconductor memory (VSM);

a second VSM; and

control circuitry operable to:

when the disk drive is powered on, first read VSM initialization code from the disk;

first initialize the first VSM using the VSM initialization code;

store the VSM initialization code in the second VSM;

enter a power save mode; and

when exiting the power save mode, second initialize the first VSM using the VSM initialization code stored in the second VSM.

2. The disk drive as recited in claim 1 , wherein when the disk drive is powered on the control circuitry is further operable to execute disk initialization code from a boot read only memory (ROM) in order to enable the reading of the VSM initialization code from the disk.

3. The disk drive as recited in claim 1 , wherein:

the control circuitry comprises a microprocessor operable to execute the VSM initialization code; and

the control circuitry is further operable to power down the microprocessor when entering the power save mode.

4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to refresh the first VSM while in the power save mode.

5. The disk drive as recited in claim 1 , wherein in connection with entering the power save mode the control circuitry is further operable to:

second read the VSM initialization code from the disk; and

store the VSM initialization code in the second VSM after second reading the VSM initialization code from the disk.

6. The disk drive as recited in claim 1 , wherein after first initializing the first VSM the control circuitry is further operable to:

first read disk drive boot code from the disk and store the disk drive boot code in the first VSM;

first execute the disk drive boot code from the first VSM prior to entering the power save mode; and

second execute the disk drive boot code from the first VSM after second initializing the first VSM.

7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to:

purge the disk drive boot code from the first VSM after first executing the disk drive boot code; and

prior to entering the power save mode, second read the disk drive boot code from the disk and store the disk drive boot code in the first VSM.

8. The disk drive as recited in claim 1 , wherein the second VSM comprises a plurality of registers.

9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to store the VSM initialization code in the second VSM by storing an address in a first register and a corresponding value in a second register.

10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to second initialize the first VSM by assigning the value stored in the second register to the address stored in the first register.

11. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to second initialize the first VSM by copying the VSM initialization code from the registers to an internal memory and executing the VSM initialization code from the internal memory.

12. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, a first volatile semiconductor memory (VSM), and a second VSM, the method comprising:

when the disk drive is powered on, first reading VSM initialization code from the disk;

first initializing the first VSM using the VSM initialization code;

storing the VSM initialization code in the second VSM;

entering a power save mode; and

when exiting the power save mode, second initializing the first VSM using the VSM initialization code stored in the second VSM.

13. The method as recited in claim 12 , wherein when the disk drive is powered on further comprising executing disk initialization code from a boot read only memory (ROM) in order to enable the reading of the VSM initialization code from the disk.

14. The method as recited in claim 12 , wherein:

the disk drive comprises a microprocessor operable to execute the VSM initialization code; and

further comprising powering down the microprocessor when entering the power save mode.

15. The method as recited in claim 12 , further comprising refreshing the first VSM while in the power save mode.

16. The method as recited in claim 12 , wherein in connection with entering the power save mode further comprising:

second reading the VSM initialization code from the disk; and

storing the VSM initialization code in the second VSM after second reading the VSM initialization code from the disk.

17. The method as recited in claim 12 , wherein after first initializing the first VSM further comprising:

first reading disk drive boot code from the disk and storing the disk drive boot code in the first VSM;

first executing the disk drive boot code from the first VSM prior to entering the power save mode; and

second executing the disk drive boot code from the first VSM after second initializing the first VSM.

18. The method as recited in claim 17 , further comprising:

purging the disk drive boot code from the first VSM after first executing the disk drive boot code; and

prior to entering the power save mode, second reading the disk drive boot code from the disk and storing the disk drive boot code in the first VSM.

19. The method as recited in claim 12 , wherein the second VSM comprises a plurality of registers.

20. The method as recited in claim 19 , further comprising storing the VSM initialization code in the second VSM by storing an address in a first register and a corresponding value in a second register.

21. The method as recited in claim 20 , further comprising second initializing the first VSM by assigning the value stored in the second register to the address stored in the first register.

22. The method as recited in claim 19 , further comprising second initializing the first VSM by copying the VSM initialization code from the registers to an internal memory and executing the VSM initialization code from the internal memory.