Emergency Unload - Hitachi 7K320 - Travelstar Mobile Hard Drive Specifications

Load/unload
6.3.6
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:
 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.
6.3.6.1

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.
6.3.6.2 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 500 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.
6.3.6.3 Power switch design considerations
In systems that use the Travelstar 7K320 consideration should be given to the design of the system
power switch.
Hitachi recommends that the switch operate under control of the BIOS, 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.
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7K320 SATA OEM Specification