Hitachi IC25N010ATCS04, Specifications

Page: 90 / 217

11.4 Power-off considerations
11.4.1 Load/Unload
Load/Unload is a functional mechanism of the hard disk drive. It is controlled by the drive microcode.
Specifically, unloading of the heads is invoked by the following commands.
UL -> Comp. Sleep
UL -> Comp. Standby Immediate
UL -> Comp. Standby
Response Command
UL -> Rdy Hard Reset
Rdy (*1) Soft Reset
Response Reset
Load/Unload condition is not changed by Soft Reset (*1)
= interface ready Rdy
= complete Comp
= unload UL
Figure 61. Device behavior by ATA commands.
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 emer-
gency mode.
11.4.2 Emergency unload
When the drive power is interrupted with the heads still loaded, the microcode cannot operate and the
normal 5V power is unavailable to unload the heads. In this case, normal unload is not possible, so 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 uncon-
trolled, it is more mechanically stressful than a normal unload.
A single emergency unload operation is more stressful than 100 normal unloads. Use of emergency un-
load reduces the start/stop life of the drive at a rate at least 100 times faster than that of normal unload
and may damage the drive.
Hitachi Travelstar 60GH & 40GN hard disk drive specifications
77