Address Offset Feature (Vendor Specific); Figure 36 Device Address Map Before And After Set Feature - Hitachi HTS541616J9AT00 - Travelstar 160 GB Hard Drive Specifications

Travelstar 5K160 (PATA) Hard Disk Drive Specification

12.10 Address Offset Feature (Vendor Specific)

Computer systems perform initial code loading (booting) by reading from a predefined address on a disk drive. To
allow an alternate bootable operating system to exist in a reserved area on a disk drive this feature provides a Set
Features function to temporarily offset the drive address space. The offset address space wraps around so that the
entire disk drive address space remains addressable in offset mode. The Set Max pointer is set to the end of the
reserved area to protect the data in the user area when operating in offset mode. This protection can be removed by
an Set Max Address command to move the Set Max pointer to the end of the drive. But any commands which access
sectors across the original native maximum LBA are rejected with error, even if this protection is removed by an Set
Max Address command.
12.10.1 Enable/Disable Address Offset Mode
Subcommand code 09h Enable Address Offset Mode offsets address Cylinder 0, Head 0, Sector 1, LBA 0, to the
start of the non-volatile protected area established using the Set Max Address command. The offset condition is
cleared by Subcommand 89h Disable Address Offset Mode, Hardware reset or Power on Reset. If Reverting to
Power on Defaults has been enabled by Set Features command, it is cleared by Soft reset as well. Upon entering
offset mode the capacity of the drive returned in the Identify Device data is the size of the former protected area. A
subsequent Set Max Address command with the address returned by Read Max Address command allows access to
the entire drive. Addresses wrap so the entire drive remains addressable.
If a non-volatile protected area has not been established before the device receives a Set Features Enable Address
Offset Mode command the command fails with Abort error status.
Disable Address Offset Feature removes the address offset and sets the size of the drive reported by the Identify
Device command back to the size specified in the last non-volatile Set Max Address command.

Figure 36 Device address map before and after Set Feature

12.10.2 Identify Device Data
Identify Device data word 83 bit 7 indicates the device supports the Address Offset Feature.
Identify Device data word 86 bit 7 indicates the device is in Address Offset mode.
12.10.3 Exceptions in Address Offset Mode
Any commands which access sectors across the original native maximum LBA are rejected with error, even if the
access protection is removed by an Set Max Address command.
Read Look Ahead operation and Write Cache Function do not be carried out while Address Offset Mode, even if it
is enabled by Set Feature command.
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