This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
LBA is a means of linearly addressing sectors addresses, beginning at sector 1 of head 0, cylinder 0 as LBA 0, and proceeding on to the last physical sector on the drive, which, for instance, on a standard 540 Meg drive would be LBA 1,065,456. This is new in ATA-2, but has always been the one and only addressing mode in SCSI. Note that LBA does not allow you to address more sectors than CHS style addressing would.
LBA reduces CPU overhead in OSs that use LBA internally, but on the other hand takes a little more time when ordinary CHS based BIOS calls are used (eg. DOS). Beware that depending on the way LBA is implemented in the harddisk firmware, the overhead on the part of the drive may increase.