Power-Off Considerations; Load/Unload; Emergency Unload; Figure 63. Device Behavior By Ata Commands - IBM IC25N020ATDA04 - Travelstar 20 GB Hard Drive Specifications

11.3 Power-off considerations

11.3.1 Load/Unload

Load/Unload is a functional mechanism of the HDD. It is controlled by the drive microcode. Specifically,
unloading of the heads is invoked by the following commands.
Command
Standby
Standby Immediate
Sleep
Reset
Soft Reset
Hard Reset
"UL" —means "unload"
"Rdy" —means "interface ready"
(*1) Load/Unload condition is not changed by Soft Reset.

Figure 63. 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.

11.3.2 Emergency unload

When HDD power is interrupted while the heads are 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
uncontrolled, it is more mechanically stressful than a normal unload.
A single emergency unload operation is more stressful than 100 normal unloads. Use of emergency
unload reduces the start/stop life of the HDD at a rate at least 100X faster than that of normal unload, and
may damage the HDD.
Response
Response
Travelstar 48GH, 30GN & 15GN hard disk drive specifications
UL -> Comp.
UL -> Comp.
UL -> Comp.
Rdy (*1)
UL -> Rdy
81