Re: int 0x13 utility
- From: "Wolfgang Kern" <spamtrap@xxxxxxxxxx>
- Date: Wed, 26 Mar 2008 13:53:39 +0100
JJ "João Jerónimo" wrote:
Alex Buell wrote:
As someone pointed already, it's pretty likely that MS-DOS 6.22 does
not support LBA routines, so it'll use CHS (which implies a maximum
of 8GB). If the SATA BIOS does not support the virtual mapping I
mentioned above in it's CHS-based routines, then you'll be even more
limited (I think it's the case).
That is *exactly* what I've been saying - I even emailed Silicon Images
about their BIOS; they might fix it or I might have to patch it myself
to put out the right numbers.
You won't still be able to access past 8GB only with CHS.
Yes INT13 CHS is somehow weird because it truncates/merges the
available hardware opportunities (28 bits) into three bytes.
16*255*4096 = 1671168 sectors (= 7.96875 GB), not to mention
that ye olde DOS often limit sectors to 63 and add the two gained
bits to the cylinder count, IMHO anyway a useless detour because
the hardware must be fed with recalculated data then.
Older BIOS has even a limit of <2GB and very old HDC can only
access <512 MB with CHS ...
But if you write your own HD-driver, the physical CHS-limit is:
16 heads, 255 sectors, 65536 tracks(cylinders), and this gives
us 267386880 sectors (= 127.5 GB).
So if the the hardware can handle it then it works almost like LBA28
(max= 128 GB), ...except for the unconvenient calculation needs.
__
wolfgang
.
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