Re: IDE disk geometry + patch

Mark Lord (
Sat, 05 Dec 1998 00:02:46 +0000

"Richard B. Johnson" wrote:
> > The number of people with 8+ GB disks increases quickly.
> > The handling of large IDE disks has always been broken,
> > but in 2.0.35 and 2.1.90 this problem was partially
> > corrected by inserting the test for C/H/S=16383/16/63.

Yes, that correction is straight from the Enhanced BIOS Specification
for handling of large disks.

> You can't have 16,383 Cylinders. There is no room in the registers
> passed to the BIOS.

There is no room to pass them to the BIOS unless extended Int13 calls
are used instead of the regular Int13 stuff.

Note that Linux itself uses LBA, not CHS, and talks directly to the
bare metal, so the only restriction there is the basic IDE disk
hardware limit of 65536 cyls, or roughly.. 128GB per drive.

The proposal from Andries would not affect Linux at all,
but does affect "fdisk" and "LILO". All appearances suggest
that the change would be a *positive* effect, in that it would
not hurt anything, and would allow linux fdisk to be used to
create partitions beyond the 1024 BIOS cyl limit.

Note that this is a BIOS-specific problem: many BIOSs do not
have this problem today with drives > 8GB (I know, I have some
drives like that, and don't have any problems).
But other BIOSs do mis-report the translated geometry.

I think there should be no problem with the change,
but urge great caution at this point in the release process.

(ex IDE guy)

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