FUJITSU DISK DRIVES MHM215OAT - Manual (Page 73)

Theory of Device Operation
4-20 C141-E104-02EN
4.7.3 Servo frame format
As the servo information, the IDD uses the two-phase servo generated from the
gray code and servo A to D. This servo information is used for positioning
operation of radius direction and position detection of circumstance direction.
The servo frame consists of 6 blocks; write/read recovery, servo mark, gray code,
servo A to D, and PAD. Figure 4.9 shows the servo frame format.
Figure 4.9 Servo frame format