Head Alignments; Head Alignment States; Head Alignment Modes - HP C2488A Technical Reference Manual

host without the delay of a media access. However, the controller is optimized to return any
requested data to the host as fast as possible.
If a new READ command requests data not contained in the buffer while the drive is
performing a Look Ahead Read, the process is aborted, and the drive will immediately seek to
the new track with no effect on access or transfer performance. Filling the track buffer with
unrequested data has a lower priority than delivering requested data, Other conditions that
may affect completing a full-track READ before receiving the next READ command are: head
position relative to the requested data, transfer size, and the host tr~nsfer rate.
Head Alignments
The drive executes periodic head alignments to maintain proper track following tolerances.
During the Power-On sequence, the drive executes a complete calibration and head alignment
for all heads. For subsequent operation, there are two modes for head alignments: the
automatic mode, and the Initiator-controlled mode. In the automatic (default) mode, the
drive automatically implements single head alignments in Seek, Read, and Write commands.
In the Initiator-controlled mode, head alignments are executed upon receipt of a Rezero Unit
command.
Head Alignment States
The drive will enter either a head alignment
needed
or
critical
state according to changes in
temperature since the last head alignment, or the elapsed time since the last head alignment.
Temperature Considerations Elapsed Time Considerations
H a temperature change exceeds the first of two factory
Under normal conditions, the drive schedules head
defined thresholds, the drive enters the head alignment alignment calibrations at preset intervals after spin-up. The
needed state. H a head alignment occurs the drive cancels drive enters the needed state at these intervals. H a head
the needed state. H the temperature change exceeds the alignment occurs the drive cancels the needed state. H twice
second (higher) threshold before a head alignment is the expected time interval passes without a calibration, the
accomplished, the drive enters the critical state.
drive enters the critical state. The time periods between
head alignments are pre-defined at the factory to assure
reliable operation under start-up and long term conditions.
Head Alignment Modes
The Mode Select command (page 09H, byte 8, bits 6 and 7), allows the Initiator to control the
head alignment function as follows:
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Product Features 3·3
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