Write Cache Function; Figure 31 Seek Overlap - Hitachi CinemaStar P7K500 Specifications

8.8 Seek Overlap
HxP7250xxGLA3y0 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, HxP7250xxGLA3y0 overlaps the seek command as
described below.
The first seek command completes before the actual seek operation is end. 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 executions of two seek
commands overlaps excluding the actual seek operation.
With this overlap, total elapsed time for a number of seek commands results the total accumulated time for
actual seek operation plus one pre and post overhead. When the number of seeks is large, this just one
overhead can be ignored.
( 1) W i t h over l ap
Host pr ocess
Devi ce pr ocess
Seek oper at i on
A
Over head
Tot al t i m e = ( n- 1) * ( Seek oper at i on) + A + B
( 2) W i t hout over l ap
Host pr ocess
Devi ce pr ocess
Seek oper at i on
Over head A
Tot al t i m e = n * ( Seek oper at i on + A + B)

8.9 Write Cache Function

Write cache is a performance enhancement whereby the device reports as completing the write command
(Write Sector(s), Write Multiple and Write DMA) to the host as soon as the device has received all of the data
into its buffer. And 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 hard reset does
not affect its operation. But power off terminates writing operation immediately and unwritten data are to
be lost.
Soft reset, Standby (Immediate) command and Flush Cache commands during writing the cached data
are executed after the completion of writing to media. So the host system can confirm the completion of
write cache operation by issuing Soft reset, Standby (Immediate) command or Flush Cache command to
the device before power off.
HITACHI Deskstar & CinemaStar P7K500 Hard Disk Drive specification (Rev 1.1)
B+A

Figure 31 Seek overlap

78
B
B