Logical block addressing
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Logical block addressing in computing maps conceptual data storage onto secondary storage. LBA is used to overcome size limits of hard drives. Another less popular method is the Extended Cylinder-Head-Sector (ECHS).
The idea is to give disk sectors linear numbers starting with 0, as opposed to classic cylinder-head-sector (CHS) addressing where disk sectors are described by their coordinates in terms of cylinders, heads and sectors, limited to 1024/4096/16384, 16/256 and 63 respectively. Original limits were 1024*16*63, but newer BIOSes can transform a coordinate system with more than 16 (virtual) disk heads into one which has more cylinders instead, or they can transform CHS coordinates in a coordinate system of up to 1024*255*63 size (limit for MS-DOS, usually corresponds to 8 GB disk size) into LBA addresses, internally communicating with the disk in terms of LBA space.
LBA addresses can be 28 bit or 48 bit wide, which results in a disk size limit of 128 GiB and 128 PiB, respectively, if you assume (very common for harddisks) 512 bytes per sector.
External links
- Logical Block Addressing (LBA) (http://www.pcguide.com/ref/hdd/bios/modesLBA-c.html) from the The PC Guide.
- Extended CHS (ECHS) / Large Mode (http://www.pcguide.com/ref/hdd/bios/modesECHS-c.html) from the The PC Guide.
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