Hitachi HTS725050A9A364 Datasheet download pdf (Page 53)

7K500 OEM Specification

Page 53 of 176

12.3

12.312.3

12.3 Power

PowerPower

Power-

-off considerations

off considerations off considerations

off considerations

12.3.1

12.3.112.3.1

12.3.1

Load/Unload

Load/Unload Load/Unload

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 commands:

Command Response

Standby UL -> Comp.

Standby immediate UL -> Comp.

Sleep UL -> Comp.

“UL” means “unload”.

“Comp” means “complete”.

Table 33 Device’s 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

emergency mode.

12.3.2

12.3.212.3.2

12.3.2

Emergency unload

Emergency unload Emergency unload

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.

12.3.3

12.3.312.3.3

12.3.3

Required power

Required powerRequired power

Required power-

-off sequence

off sequence off sequence

off sequence

Problems can occur on most HDDs when power is removed at an arbitrary time. Examples:



Data loss from the write buffer.



If the drive is writing a sector, a partially-written sector with an incorrect ECC block results. The sector

contents are destroyed and reading that sector results in a hard error.



Heads possibly land in the data zone instead of landing zone, depending on the design of the HDD.

You may then turn off the HDD in the following order:

Issue Standby Immediate or sleep command.

Wait until COMMAND COMPLETE STATUS is returned. (It may take up to 350 ms in typical case)

Terminate power to HDD.

This power-down sequence should be followed for entry into any system power-down state, or 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.

12.4

12.412.4

12.4 Sector Addressing Mode

Sector Addressing Mode Sector Addressing Mode

Sector Addressing Mode

All addressing of data sectors recorded on the device’s media is by a logical sector address. The

logical CHS address for HTS7250XXA9A3XX is different from the actual physical CHS location of

the data sector on the disk media.

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Hitachi HTS725050A9A364 Datasheet Page 53

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