Hitachi HDS721050CLA362 Specifications page 228

Output Parameters To The Device
Sector Count Timeout Parameter. If zero, the timeout interval (Standby Timer) is NOT disabled. If
non-zero, then the automatic power down sequence is enabled, and the timeout
interval is shown blow:
When the automatic power down sequence is enabled, the drive will enter Standby
mode automatically if the timeout interval expires with no drive access from the host.
The timeout interval will be reinitialized if there is a drive access before the timeout
interval expires.
HITACHI Deskstar & CinemaStar 7K1000.B & Deskstar E7K1000 Hard Disk Drive specification
Value Timeout
------------ -------------------------------
0 Timer disabled
1-240 Value * 5
241-251 (Value-240) * 30 minutes
252 21 minutes
253 8 hours
254 21 minutes 10 seconds
255 21 minutes 15 seconds
224
seconds