Disk drive comprising preamble aligned zoned servo sectors

1. A disk drive comprising:

a disk comprising a plurality of servo sectors defining a plurality of servo tracks, and a head actuated radially over the disk for generating a read signal, wherein:

each servo sector comprises a preamble comprising a first end and a second end;

each servo sector comprises a servo sync mark after the second end of the preamble;

the servo tracks form a plurality of servo zones;

a servo data rate of the servo sectors in a first servo zone is different than a servo data rate of the servo sectors in a second servo zone;

the first end of the preambles in the servo sectors are aligned along a radius of the disk across at least the first servo zone and the second servo zone;

the disk drive further comprising control circuitry operable to:

generate a servo clock;

open a servo gate window in response to the servo clock when the head approaches one of the servo sectors;

when the head transitions between the first servo zone and the second servo zone, adjust the servo gate window; and

demodulate the servo sector,

wherein the control circuitry is further operable to adjust an end of the servo gate window.

2. The disk drive as recited in claim 1 , wherein the servo clock comprises a first rate when opening the servo gate window in the first servo zone and comprises the first rate when opening the servo gate window in the second servo zone.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the servo gate window after reading at least part of the preamble in a servo sector in the second servo zone.

4. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of servo sectors defining a plurality of servo tracks, and a head actuated radially over the disk for generating a read signal, wherein:

each servo sector comprises a preamble comprising a first end and a second end;

each servo sector comprises a servo sync mark after the second end of the preamble;

the servo tracks form a plurality of servo zones;

a servo data rate of the servo sectors in a first servo zone is different than a servo data rate of the servo sectors in a second servo zone; and

the first end of the preambles in the servo sectors are aligned along a radius of the disk across at least the first servo zone and the second servo zone;

the method comprising:

generating a servo clock;

opening a servo gate window in response to the servo clock when the head approaches one of the servo sectors;

when the head transitions between the first servo zone and the second servo zone, adjusting the servo gate window; and

demodulating the servo sector,

wherein adjusting the servo gate window comprises adjusting an end of the servo gate window.

5. The method as recited in claim 4 , wherein the servo clock comprises a first rate when opening the servo gate window in the first servo zone and comprises the first rate when opening the servo gate window in the second servo zone.

6. The method as recited in claim 4 , further comprising adjusting the servo gate window after reading at least part of the preamble in a servo sector in the second servo zone.

7. A disk drive comprising:

a disk comprising a plurality of servo sectors defining a plurality of servo tracks, and a head actuated radially over the disk for generating a read signal, wherein:

each servo sector comprises a preamble comprising a first end and a second end;

each servo sector comprises a servo sync mark after the second end of the preamble;

the servo tracks form a plurality of servo zones;

a servo data rate of the servo sectors in a first servo zone is different than a servo data rate of the servo sectors in a second servo zone; and

the first end of the preambles in the servo sectors are aligned along a radius of the disk across at least the first servo zone and the second servo zone;

the disk drive further comprising control circuitry operable to:

generate a servo clock;

open a servo gate window in response to the servo clock when the head approaches one of the servo sectors;

when the head transitions between the first servo zone and the second servo zone, adjust the servo gate window; and

demodulate the servo sector,

wherein:

the control circuitry is further operable to adjust an interval between servo gate windows;

the servo clock comprises a variable rate adjusted relative to the servo data rate of the servo zone; and

the control circuitry is further operable to adjust the rate of the servo clock relative to the servo data rate of the second servo zone after reading at least part of the preamble in a servo sector in the second servo zone.

8. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of servo sectors defining a plurality of servo tracks, and a head actuated radially over the disk for generating a read signal, wherein:

each servo sector comprises a preamble comprising a first end and a second end;

each servo sector comprises a servo sync mark after the second end of the preamble;

the servo tracks form a plurality of servo zones;

a servo data rate of the servo sectors in a first servo zone is different than a servo data rate of the servo sectors in a second servo zone; and

the first end of the preambles in the servo sectors are aligned along a radius of the disk across at least the first servo zone and the second servo zone;

the method comprising:

generating a servo clock;

opening a servo gate window in response to the servo clock when the head approaches one of the servo sectors;

when the head transitions between the first servo zone and the second servo zone, adjusting the servo gate window; and

demodulating the servo sector,

wherein:

adjusting the servo gate window comprises adjusting an interval between servo gate windows;

the servo clock comprises a variable rate adjusted relative to the servo data rate of the servo zone; and

the method further comprises adjusting the rate of the servo clock relative to the servo data rate of the second servo zone after reading at least part of the preamble in a servo sector in the second servo zone.