Datasheet

12.8 Seek Overlap

The drive provides an 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, the drive overlaps 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.

(1) With overlap

(2) Without overlap

Host process

Device process

Seek operation

Overhead

AB+A

B+A

Total time = (n-1) * (Seek operation) + A + B

Total time = n * (Seek operation + A + B)

Figure 67. Seek overlap

12.9 Write Cache Function

Write cache is a performance enhancement whereby the device reports completion of the write command

(WRITE SECTORS and WRITE MULTIPLE) to the host as soon as the device has received all of the

data into its buffer. The device assumes responsibility for writing the data subsequently onto the disk.

y While writing data after a completed acknowledgment of a write command, a soft reset, or a hard

reset does not affect its operation. However, a power off terminates the writing operation immedi-

ately and unwritten data gets lost.

y FLUSH CACHE, SOFT RESET, STANDBY, STANDBY IMMEDIATE and SLEEP are executed after

the completion of a writing to disk media on enabling write cache function. So the host system can

confirm the completion of the write cache operation by issuing FLUSH CACHE command, SOFT

RESET, STANDBY command, and STANDBY IMMEDIATE command and then confirming the com-

pletion.

y The retry bit of WRITE SECTORS is ignored when write cache is enabled.

Hard disk drive specification for DSCM-11000/-10512/-10340