11.11
Seek Overlap
The drive provides accurate seek time measurement method. The seek command is usually used to
measure the device seek time by accumulating execution time for a number of seek commands. With
typical implementation of the seek command, this measurement must include the device and host com-
mand overhead. To eliminate this overhead, the drive overlaps the seek command as described below.
The first seek command completes before the actual seek operation is over. Then the device can receive
the next seek command from the host. However, actual seek operation for the next seek command starts
right after completion of the actual seek operation for the first seek command. The execution of two seek
commands overlaps excluding the actual seek operation.
With this overlap, total elapsed time for a number of seek commands is the total accumulated time for the
actual seek operation plus one pre and post overhead. When the number of seeks is large, this overhead
can be ignored.
(1) With overlap
(2) Without overlap
Host process
Host process
Device process
Device process
Seek operation
Seek operation
Overhead
Overhead
A
AB+A
B
B+A
B
Total time = (n-1) * (Seek operation) + A + B
Total time = n * (Seek operation + A + B)
Figure 72. Seek overlap
Travelstar 48GH, 30GN & 15GN hard disk drive specifications
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