IBM DBCA-204860 Hard Drive Specifications - Page 92

Address Offset Feature Vendor Specific

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10.9 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. 10.9.1 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. 84 OEM Specifications of DBCA-2xxxxx 2.5 inch H D D

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10.9
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.
10.9.1
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 Iden-
tify Device command back to the size specified in the last non-volatile Set Max Address command.
84
OEM Specifications of DBCA-2xxxxx 2.5 inch HDD