🚀 go-pugleaf

svolaf@inet.uni2.dk (Svend Olaf Mikkelsen) wrote:

> "Rod Speed" <rod_speed@yahoo.com> wrote:
> 
> >> This is a really nasty bug.

> >You appear to be confusing the undoubted problem with changes
> >to the mapping between the CHS values and the LBA block numbers
> >that can certainly vary with the OS level mapping, and what the bios
> >does at boot time with an AUTO drive type, what was being discussed.
 
> The OS has nothing to do with this. Let me give you an example.
 
> Award BIOS with extended interrupt 13h (disk) support. A 9671 MB IDE
> harddisk. The disk is set to User/LBA, and the disk has a BIOS
> translation of 1232 cylinders, 255 heads, 63 sectors. With this
> translation 9664 MB are useable.
 
> A 9664 MB partition is created. The partition table is correct, and
> assumes a 255 heads translation.
 
> The disk has 19,807,200 sectors. We look at LBA sector 10,000,000
> (numbered from 0). This will be
 
> cylinder 622, head 120, sector 11
 
> Then we reboot, and enter BIOS setup. LBA mode is changed to NORMAL
> mode. A translation of 19650 cylinders, 16 heads, 63 sectors is
> displayed. We save the change and boot.
 
> Then we request the disk geometry by calling BIOS interrupt 13h. The
> answer is 1232 cylinders, 255 heads, 63 sectors.
 
> Then we call BIOS interrupt 13h, function 42h, and request LBA sector
> 10,000,000. A sector is returned.
 
> Everything looks OK, but it is definitely not sector 10,000,000 that
> is returned.
 
> Then we use interrupt 13h, function 02h, to request cylinder 622, head
> 120, sector 11.
 
> Again: Everything looks OK, but it is definitely not sector 10,000,000
> that is returned.
 
> Please note that this is only one of the Award bugs. The one that I
> called nasty.

This isn't a bug, it's a feature, incorporated in these BIOSes, for a
purpose.

Regards, Zvi
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