Logical Block Addressing

The term logical block addressing ( LBA) or English Logical Block Addressing refers to a method of addressing at ATA hard drives.


The blocks of the hard disk will be completely addressed independently from the hard disk geometry as opposed to the three-dimensional cylinder - head - sector addressing ( engl. Cylinder -Head -Sector, shortly CHS). The blocks are at the LBA method simply counted, starting with zero. Each LBA block corresponds to a single sector of the CHS addressing.

In LBA bit distinguishes between addresses 28 and 48. A 28 -bit LBA address allows addressing of 268,435,456 blocks. In the conventional block and sector size of 512 bytes is equal to the 128 GiB. As an extension of a 48 -bit address (48 -bit LBA or Big LBA ) is introduced at 6 ATA, the 281,474,976,710,656 blocks (ie 128 PIB) can be addressed.

48 -bit LBA is used in hard drives with capacities of more than 128 GiB used if the BIOS also 48 -bit LBA support.

In relation to the size of the CDB ( Command Descriptor Block) and 32- bit and 64-bit LBA - LBA (long LBA) is spoken. This is due to the fact that only 4 bytes ( 32 bits) are provided for the address in LBA 10 byte CDB. Thus, a maximum of 232 = 4,294,967,296 blocks and are addressed with a Block-/Sektorgröße of 512 bytes up to 2 TiB. Another limitation to 32 -bit LBA addressing and the resulting 2- TiB limit is justified in the construction of the partition table of the MBR.

With the expansion of CDB length to 16 or 32 bytes 8 bytes ( 64 bits ) are provided for the LBA address.

Support in operating systems

Current operating systems (eg Microsoft Windows 7, Linux, BSD) do not require additional adjustments to enable 48 -bit LBA.

Situation with older operating systems

When using older versions of Windows, there may be problems, as 48 -bit LBA is not used by default until version Windows XP ( Service Pack 1). In the original version of Windows XP ( no service pack), it must be enabled manually. The same applies to Windows 2000: Here is next to the manual activation of at least Service Pack 3 is required.

Been For Windows 98 and Windows Me there is no part of Microsoft 48 -bit LBA support, but there are various free or fee-based solutions developed by individuals or companies ( eg Intel hard disk Accelerator for motherboards with Intel chipset ).

When using hard disks with more than 128 GiB of systems without 48 -bit LBA support, there is the danger that a break occurs at the beginning of the disk, where the Master Boot Record and the first partition will be overwritten. This has result in data loss.

For Windows 2000, as well as in the original version of Windows XP ( no service pack) must (of type REG_DWORD to find under HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ atapi \ Parameters \ ) are activated in the Windows registry key EnableBigLba - either entered manually and set it to 1, or by running a tool like EnableBigLba.exe that performs this entry. Versions of Windows from XP with Service Pack 1 ignore this key and enable support always.

During the installation of Windows XP, it can get the error message " Error loading operating system " after the installation routine has finished installing copied to the hard disk and before she restarts the computer before the actual installation process. This may occur if the BIOS has problems with 48 -bit LBA.

Since Windows Server 2003 Service Pack 1 and Windows XP 64- Bit Edition Microsoft also supports long LBA.