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8.7 Servo Control
C141-E133-02EN 8-11
1) Dead space
The dead space is at the innermost position of a disk. At spindle start and stop, the head is in
contact with this area of the disk.
2) Inner guard band (IGB)
IGB is located in an inner position of a disk. IGB is used to detect that actuator operation has
exceeded the ordinary seek operation range.
3) Data zone
The servo zone is the data recording part on the data side. Ordinary head seek operations are
done within this zone.
4) Outer guard band (OGB)
OGB is located in an outer position of a disk. Like IGB, OGB is also used to detect that actuator
operation has exceeded the ordinary seek operation range.
(2) Frame format
The servo pattern consists of 120 servo frames per one revolution. One servo frame is divided into 4
areas and these areas are separated with a gap. Figure 8.6 shows the servo frame configuration.
1) Training area
The training area consists of a fixed-period burst signal and has following functions.
•
Preparation of servo mark detection
•
Gap
2) Servo mark area
Servo mark patterns are written in the servo mark areas and patterns are detected by the length of
the DC areas. The servo mark determines the starting point for detecting a position pattern and
gray code pattern.
3) Gap area
The gap area is located before and after the gray code area and position area. The gap area
prevents the misdetection of the gray code pattern or position pattern by releasing a
synchronization of the servo mark or delaying a reference counter.