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)