LBA

from The Free On-line Dictionary of Computing (8 July 2008)
Logical Block Addressing
LBA

   <storage> (LBA) A {hard disk} {sector} addressing scheme used
   on all {SCSI} hard disks, and on {ATA-2} conforming {IDE} hard
   disks.  The addressing conversion is performed by the hard
   disk firmware.

   Prior to LBA, combined limitations of {IBM PC} {BIOS} and
   {ATA} restricted the useful capacity of IDE hard disks on IBM
   PCs and compatibles to 1024 cylinders * 63 sectors per track *
   16 heads * 512 bytes per sector = 528 million bytes = 504
   megabytes.  Modern BIOSes select LBA mode automatically, and
   work around the 1024-cylinder BIOS limit by representing a
   hard disk to the OS as having e.g. half as many cylinders and
   twice as many heads.  However, there is still an unbreakable
   BIOS disk size limit of 1024 cylinders * 63 sectors per track
   * 256 heads * 512 bytes per sector = 8 gigabytes, but modern
   OSes (including {Windows 9x}, {Windows NT} and {Linux}) are
   not affected by it, since they issue direct LBA-based calls,
   bypassing the BIOS hard disk services completely.

   (2000-04-30)