Re: Another multibooting option for the FAQ

There are probably 20 different ways to go about dual booting.  However, 
the OpenBSD FAQ is not going to spend much time on saying how to use 
Windows to accomplish something.  I set up a dual boot machine 
recently, because I needed to use something on Windows, and I wrote a 
script to copy a modified first sector to the single hard drive, followed 
by a reboot, and so then just do a:

sudo win

to go to Windows.

Then on Windows I installed Cygwin where I made a script that does the 
reverse, which I run as "./openbsd", which causes any subsequent reboot to 
return to OpenBSD.

I'll leave it to you to figure out how to use dd and a hex editor to 
toggle the one byte in a copy of that first sector that makes the crucial 
difference.  The hardest thing for me was to figure out how cygwin could 
refer to the raw disk at sector 1 track 0 head 0.   I suppose there are 
utilities somewhere that could avoid using Cygwin (a Unix like subsystem 
to works on Windows), and just do the same thing and reboot directly.

I don't figure there is much danger changing the first sector, if the 
criitial step is run under a script, so I don't think fancy dual booting 
code or bios's are necessary.

Austin


On Thu, 13 May 2010, John Danks wrote:

> I just realized this one recently. Most modern BIOS allow you to press
> a key on the POST screen and choose a boot device, even a specific
> hard drive.
>
> All of the current multiboot options in the FAQ describe methods for
> use with a single disk. An alternative then is to install Windows on
> the first disk which the BIOS boots to by default, and then install
> OpenBSD on a separate disk in the same machine. Simply press F10, F12
> or whatever key your BIOS uses and choose the OpenBSD disk as your
> boot device.
>
> This method saves you the trouble of messing around with partitions,
> bootloaders and potential data loss, assuming you have an additional
> drive, room in the case to install it and a BIOS that supports the
> option to choose an alternate boot device.