Hardware Reference
In-Depth Information
LBA-Assist Translation
The LBA-assist translation method places no artificial limits on the reported drive geo-
metries, but it works only on drives that support LBA addressing at the ATA interface
level. Fortunately, though, virtually all ATA drives larger than 2GB support LBA. LBA-
assist translation takes the CHS parameters the drive reports, multiplies them together to
get a calculated LBA maximum value (total number of sectors), and then uses this calcu-
lated LBA number to derive the translated CHS parameters.
Table 7.21
shows the rules
for LBA-assist translation.
Table 7.21 LBA-Assist Translation Rules
LBA-assist translation fixes the sectors at 63 no matter what and divides and multiplies
thecylindersandheadsbypredeterminedvaluesdependingonthetotalnumberofsectors.
This results in a set of L-CHS parameters the operating system uses to communicate with
the BIOS. The L-CHS numbers are then translated to LBA numbers at the ATA interface
level. Because LBA mode is more flexible at translating, you should use it in most cases
instead of CHS bit-shift.
Normally, both the CHS bit-shift and LBA-assist translations generate the same L-CHS
geometry for a given drive. This should always be true if the drive reports 63 sectors per
track and 4, 8, or 16 heads. In the following example, both translation schemes result in
identical L-CHS values:
Revised bit-
LBA-assist
P-CHS
shift L-CHS
L-CHS
Parameters
Parameters
Parameters
——————————————————————————————-
Cylinders 8,192 1,024 1,024
Heads 16 128 128
Sectors/Track 63 63 63
=============================================================
Total Sectors
8,257,536
8,257,536
8,257,536
——————————————————————————————-
