LBA
       Logical Block Addressing (EIDE)

	

	Logical Block Addressing
LBA

    (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)