Seek Time; Multisegmented Cache Buffer - Seagate ST3780A Product Manual

4

1.3 Seek time

Seek time is the interval between the time the actuator begins to move
and the time the head has settled over the target track. Seek time is a
true statistical average of at least 5,000 measurements of seek time. All
measurements are taken under nominal conditions of temperature and
voltage with the drive mounted horizontally. The specifications in the
table below are defined as follows:
• Track-to-track seek time is the average of all possible single-track
seeks in both directions.
• Average seek time is measured by executing seeks in both directions
between random cylinders.
• Full-stroke seek time is half the time needed to seek from track 0 to
the maximum track and back to track 0.
Track-to-track Average/typical
seek time seek time
3.5 msec typ 12.0 msec read
4.5 msec max 14.0 msec write
Note. Host overhead varies between systems and cannot be specified.
Drive internal overhead is measured by issuing a no-motion seek.
Overhead is typically less than 0.5 msec.

1.3.1 Multisegmented cache buffer

The drive uses the 256-Kbyte multisegmented cache buffer to improve
performance by eliminating access times under certain conditions.
Read look-ahead. The drive uses the read segments to store additional
logical sectors, after the last requested sector, into a buffer before the
computer requests the additional sectors. The cache buffer stores data
from the start of a read until the buffer segment is full or until another
command is received.
Write immediate. The drive uses the write segment to store write
commands and data. After the drive receives all of the data for the
command, it issues a write complete. Then, the drive writes the data to
the disc.
Write merging. The drive accepts contiguous write commands and
executes them as one command.
Medalist Family AT Product Manual, Rev. A
Full-stroke
seek time
25.0 msec typ
27.0 msec max
Average
latency
6.67 msec