Seek Overlap; Write Cache Function; Reassign Function; Figure 9 Seek Overlap - Hitachi HTS542516K9SA00 Specifications

12.11

Seek Overlap

HTS5425XXK9SA00 / HTS5425XXK9A300 provide 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 including the device and host command overhead. To eliminate this overhead,
HTS5425XXK9SA00 / HTS5425XXK9A300 overlap the seek command as described below.
The first seek command completes before the actual seek operation is over. Then device can receive
the next seek command from the host but actual seek operation for the next seek command starts
right after the actual seek operation for the first seek command is completed. In other words, 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, just
this one overhead can be ignored.

Figure 9 Seek overlap

12.12

Write Cache Function

Write cache is a performance enhancement whereby the device reports completion of the write
command (Write Sector(s) and Write Multiple) to the host as soon as the device has received all of
the data into its buffer. The device assumes responsibility to write the data subsequently onto the
disk.
While writing data after completed acknowledgment of a write command, soft reset or COMRESET does
not affect its operation. But power off terminates writing operation immediately and unwritten data are to
be lost.
Flush cache, Soft reset, Standby, Standby Immediate and Sleep are executed after the completion of
writing to disk media on enabling write cache function. So the host system can confirm the completion of
write cache operation by issuing flush cache command, Soft reset, Standby command, Standby Immediate
command or Sleep command, and then, by confirming its completion.
12.13

Reassign Function

The reassign Function is used with read commands and write commands. The sectors of data for
reassignment are prepared as the spare data sector. The one entry can register 256 consecutive
sectors maximally.
This reassignment information is registered internally, and the information is available right after
completing the reassign function. Also the information is used on the next power on reset.
If the number of the spare sector reaches 0 sector, the reassign function will be disabled
automatically.
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5K250 (SATA) OEM Specification