Logical block addressing

Logical block addressing in computing maps conceptual data storage onto secondary storage. LBA is used to overcome size limits of hard drives.

See hard disk.

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 2 TB (2048 GB) and 128 EB (wow!) respectively if you assume (very common for harddisks) 512 bytes per sector.