[OpenBIOS] Support for 16 head harddisk on OLD Interactive Unix configured for 15 head harddisk

Lennart Sorensen lsorense at csclub.uwaterloo.ca
Tue Oct 6 19:49:13 CEST 2009

On Tue, Oct 06, 2009 at 10:10:10AM +0200, Hanusz L. wrote:
> I have an old system running Interactive Unix on a 15 head harddisk (4Gb).
> I would like to clone this system to a 16 head harddisk because it is now difficult to find 15 head harddisks.
> The problem is that I cannot modify the system which think it has a 15 head harddisk.
> I suppose that Interactive unix use the Int13 interrupt mechanism to access the disk (am I wrong ?).

I highly suspect you are wrong.  DOS uses INT13.  Boot loaders use INT13.
Anything runing protected mode does not.  Anything 32bit is protected mode.

> I wonder if there is a possibility to modify openbios so that a 16 head harddisk is used and is simulated as a 15 head harddisk by the bios ?
> I would probably have to modify the drivers/ide.c file to do a conversion.
> My questions are:
> -          Can openbios boot Interactive Unix ?
> -          What implementation should I use ?
> Thanks for any help,

Are you running this on real hardware or on qemu or what?  If the OS
actually uses CHS access to the disk, then I don't think you can do
anything on real hardware since the disk isn't likely to help you out
translating.  If the OS actually uses LBA (as most sane OSs have done for
many years), then it doesn't matter and the CHS is just partition table
related and doesn't do anything after the partitions have been located.

I am sure qemu could be made to emulate a disk with any desired geometry

If real hardware, well replacing the BIOS on a system is a lot of hard
work given you have to figure out all the hardware initialization that
must be done.  It still doesn't solve the fact that the disk when
receiving CHS based commands isn't going to be 15 heads.

Len Sorensen

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