Emergency Unload - Hitachi HTS541616J9AT00 - Travelstar 160 GB Hard Drive Specifications

6.3.6 Load/unload
The product supports a minimum of 600,000 normal load/unloads.
Load/unload is a functional mechanism of the hard disk drive. It is controlled by the drive micro code. Specifically,
unloading of the heads is invoked by the following commands:
Hard reset
Standby
Standby immediate
Sleep
Load/unload is also invoked as one of the idle modes of the drive.
The specified start/stop life of the product assumes that load/unload is operated normally, not in emergency mode.
6.3.7

Emergency unload

When hard disk drive power is interrupted while the heads are still loaded the micro code cannot operate and the
normal 5-volt power is unavailable to unload the heads. In this case, normal unload is not possible. The heads are
unloaded by routing the back EMF of the spinning motor to the voice coil. The actuator velocity is greater than the
normal case and the unload process is inherently less controllable without a normal seek current profile.
Emergency unload is intended to be invoked in rare situations. Because this operation is inherently uncontrolled, it
is more mechanically stressful than a normal unload.
The drive supports a minimum of 20,000 emergency unloads.
6.3.8 Required Power-Off Sequence
The required host system sequence for removing power from the drive is as follows:
Step 1: Issue one of the following commands.
Standby
Standby immediate
Sleep
Note: Do not use the Flush Cache command for the power off sequence because this command does
not invoke Unload.
Step 2: Wait until the Command Complete status is returned.
In a typical case 350 ms are required for the command to finish completion; however, the host system time out
value needs to be 30 seconds considering error recovery time. Refer to section 14.0, "Time-out values," on page
193.
Step 3: Terminate power to HDD.
This power-down sequence should be followed for entry into any system power-down state, system suspend state,
or system hibernation state. In a robustly designed system, emergency unload is limited to rare scenarios, such
as battery removal during operation.
6.3.9 Power switch design considerations
In systems that use the Travelstar 5K160 consideration should be given to the design of the system power switch.
HITACHI recommends that the switch operate under control of the host system, as opposed to being hardwired. The
same recommendation is made for cover-close switches. When a hardwired switch is turned off, emergency unload
occurs, as well as the problems cited in section 5.1, "Data loss by power off" on page 19 and section 5.2, "Write
Cache" on page 19.
Travelstar 5K160 (PATA) Hard Disk Drive Specification
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