Hardware Reference
In-Depth Information
Total Bytes 6,193,152,000 6,193,152,000 6,193,152,000
Megabytes (MB) 6,193 6,193 6,193
Mebibytes (MiB) 5,906 5,906 5,906
Gigabytes (GB) 6.19 6.19 6.19
Gibibytes (GiB) 5.77 5.77 5.77
As you can see from this example, a drive with 12,000 cylinders and 16 heads translates
to750cylindersand256headsusingthestandardCHSbit-shiftscheme.TherevisedCHS
bit-shift scheme rule does a double translation in this case, first changing the 16 heads
to 15 and then multiplying the 12,000 cylinders by 16/15, resulting in 12,800 cylinders.
Then, the new cylinder value is CHS bit-shift-translated (it is divided by 16), resulting in
800logicalcylinders.Likewise,the15headsaremultipliedby16,resultingin240logical
heads. If the logical cylinder count calculates to more than 1,024, it is truncated to 1,024.
Inthiscase,whatstarted outas12,000cylinders and16headsP-CHSbecomes 800cylin-
ders and 240 heads (instead of 750 cylinders and 256 heads) L-CHS, which works around
the bug in the DOS/Win9x/Me operating systems.
So far, all my examples have been very clean—that is, the L-CHS parameters have calcu-
latedtothesamecapacityastheP-CHSparameters.Unfortunately,itdoesn'talwayswork
out that way. The following example shows a more typical example in the real world.
Several 8.4GB drives fromMaxtor,Quantum, Seagate, andothers report 16,383cylinders
and 16 heads P-CHS. For those drives, the translations would work out as follows:
Bit-shift
Revised Bit-
P-CHS
L-CHS
shift L-CHS
Parameters
Parameters
Parameters
——————————————————————————————-
Cylinders 16,383 1,023 1,024
Heads 16 256 240
Sectors/Track 63 63 63
=============================================================
Total Sectors
16,514,064
16,498,944
15,482,880
——————————————————————————————-
Total Bytes 8,455,200,768 8,447,459,328 7,927,234,560
Megabytes (MB) 8,455 8,447 7,927
Mebibytes (MiB) 8,064 8,056 7,560
Gigabytes (GB) 8.46 8.45 7.93
Gibibytes (GiB) 7.87 7.87 7.38
Note that the revised CHS bit-shift translation rules result in supporting only 7.93GB of
the8.46GBtotalonthedrive.Infact,theparametersshown(with240heads)aretheabso-
lute maximum that revised CHS bit-shift supports. Fortunately, another translation mode
is available that improves this situation.
