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Re: Hard Disk Partition Recovery

On Mon, Jan 27, 2003 at 09:53:36AM +0100, Rogier Wolff wrote:
> On Sun, Jan 26, 2003 at 09:59:07PM -0500, Barry Pollock wrote:
> > Keep in mind that dos 6.22 is only a 16 bit system and linux is 32 bit so
> > if a 32  bit system writes to the partition table a  16 bit system may not
> > be able to access the boot secter. keep  in mind that dos can only read 2
> > partitions from the primary 

Not true - see later

> and linux can read 4
> Ehmm. You can do 32 bit math with a 16 bit processor, if required. Just
> like you can do 64 bit math on a 32bit processor. 
>    main (){long long t; t=111111111; t=t*t; printf ("%lld\n",t); }
> Now I will agree that creating partition tables with Linux may make
> them inaccessible to Windows. But this seems to be a simple consistency
> check in Windows that somehow seems to trigger. Not a fundamental 16/32
> bit issue. 

It seems to be a CHS-LBA translation issue. The translations used by
Linux, Windoze, and the BIOS do not necessarily agree. Windoze seems
to go by the BIOS, whereas Linux can work it out for itself, and
doesn't always get the same answer as the BIOS.

BIOS CHS-LBA translations are annoyingly inconsistent. It is possible
to take an HD out of one machine and put it into another with a
different version of the same BIOS, and find that Windoze won't boot
because the BIOS is using a slightly different translation from the
old machine, and the MBR code can't find the Windoze boot sector.
Linux doesn't notice any difference.

> Also it is not true that Windows can only use 2 out of 4 primary partitions.   
> It used to be the case that windows couldn't use more than ONE primary
> partition. Just because microsoft decides "why for god's sake would
> you need more than one partition"?
> By the time they realized that this was wrong, they implemented ONLY
> extended partitions. 

Microsoft's docs go on about how YOU CAN ONLY HAVE ONE PRIMARY
TRIGGER A NUCLEAR RETALIATORY STRIKE. In practice it seems that the
only reason you "can't" have more than one primary partition is that
Microsoft fdisk won't LET you create more than one. If you use a
sector editor or similar to create four primary DOS partitions, it
doesn't seem to cause a problem either to DOS or to Windoze.

My favourite method of dual-booting Windoze and DOS is to have two
primary DOS partitions, one with DOS 6.22 and one with Windoze 98, and
use a little program to switch the bootable flag between the two
partitions. Works fine.


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