Maxtor D540X-4K - Manual (Page 60)

Basic Principles of Operation
5-12 Maxtor D540X-4K 20.4/40.0/60.0/80.0 GB AT
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In the ID-less environment, the drive’s track and cylinder skewing will be based in
unit of wedges instead of the traditional sectors. The integrated µprocessor, disk
controller and ATA interface contains a “Wedge Skew Register” to assist in the task
of skewing, where the skew offset must now be calculated with every read/write
operation. The firmware will program the skew offset into this register every time the
drive goes to a new track. The integrated µprocessor, disk controller and ATA
interface will then add this value to the wedge number in the ID calculator, effectively
relocating the “first” sector of the track away from the index. For example, if without
skew, sector 0 is to be found following wedge 0, then if the skew register is set to 10,
sector 0 will be found following wedge 10.
Since the wedge-to-wedge time is constant over the entire disk, a single set of head
and cylinder skew off-sets will fulfill the requirement for all recording zones.
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6CDNG   Skew Offsets
0QVG The switch time is calculated on the basis of the normal wedge-
to-wedge time with the spindle speed variation accounted for.
Wedge offsets are rounded to the closest whole number.
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Since the wedge-to-wedge time is constant over the entire disk, a single set of head
and cylinder skew offsets will fulfill the requirement for all recording zones. The
formula used to compute the wedge skew for a given cylinder and head is:
Wedge skew = [C* ((# of heads – 1) * TS + CS) + H * TS] MOD 180
Where:C = Cylinder number
H = Head number
TS = Head Skew Offset
CS Cylinder Skew Offset
(wedges/track = 200)
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Head Skew 2 ms 45
Cylinder Skew 1 ms 36