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Western Digital Hard Disk Drive OEM Specification
9.7
Host Protected Area Feature
Host Protected Area Feature is to provide the ‘protected area’ which cannot be accessed via conventional method.
This ‘protected area’ is used to contain critical system data such as BIOS or system management information. The
contents of entire system main memory may also be dumped into ‘protected area’ to resume after system power off.
The LBA/CYL changed by following command affects the Identify Device Information.
The following set of commands is implemented for this function.
Read Native Max ADDRESS
(‘F8’h)
Set Max ADDRESS
(‘F9’h)
9.7.1
Example for Operation (in LBA mode)
Assumptions:
For better understanding, the following example uses actual values for LBA, size, etc. Since it is just an example,
these values could be different.
Device characteristics
Capacity (native)
:
6,498,680,832 byte (6.4GB)
Max LBA (native)
:
12,692,735 (0FFFFFh)
Required size for protected area
:
206,438,400 byte
Required blocks for protected area
:
403,200 (062700h)
Customer usable device size
:
6,292,242,432 byte (6.2GB)
Customer usable sector count
:
12,289,536 (BB8600h)
LBA range for protected area
: BB8600h to C1ACFFh
1.
Shipping HDDs from HDD manufacturer
When the HDDs are shipped from HDD manufacturer, the device has been tested to have usable capacity of
6.4GB besides flagged media defects not to be visible by system.
2.
Preparing HDDs at system manufacturer
Special utility software is required to define the size of protected area and store the data into it.
The sequence is:
Issue Read Native Max Address command to get the real device maximum LBA. Returned value shows that
native device Maximum LBA is 12,692,735 (C1ACFFh) regardless of the current setting.
Make entire device be accessible including the protected area by setting device Maximum LBA as
12,692,735 (C1ACFFh) via Set Max Address command. The option could be either nonvolatile or volatile.
Test the sectors for protected area (LBA >= 12,289,536 (BB8600h)) if required.
Write information data such as BIOS code within the protected area.
Change maximum LBA using Set Max Address command to 12,289,535 (BB85FFh) with nonvolatile option.
From this point, the protected area cannot be accessed till next Set Max Address command is issued. Any
BIOSes, device drivers, or application software access the HDD as if that is the 6.2GB device because the
device acts exactly the same as real 6.2GB device does.
3.
Conventional usage without system software support
Since the HDD works as 6.2GB device, there is no special care to use this device for normal use.
