EDIT:This thread is now largely irrelevant, as 7.04 has an "Advanced" button at the Grub installation stage, which when pressed gives the option to enter a different location for Grub to be written to.
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Generally in Ubuntu EDIT: up to6.10? the usual way to install a dual-boot system involves overwriting the Master Boot Record of the Windows hard drive.
On one hard drive this is pretty much unavoidable.
If you are dual-booting with TWO hard drives it is not necessary to write Grub over the MBR if you can access a "Boot Device Selection Menu" by pressing F8
(or whatever key depending on BIOS)
You can thus keep both installations entirely separate.
To do it this way:
Disconnect the Windows drive and install Ubuntu and Grub on the second drive. Reconnect first drive after installing Ubuntu.
Windows on master, Ubuntu & Grub on slave if using two IDE drives.
(This method will also work on SATA drives, or a mix of SATA & IDE)
Press F8 (or whatever key depending on BIOS version) at boot time to bring up the Boot Device Selection Menu.
Choose OS by selecting which drive to boot from.
Select desired default OS by re-arranging boot order in BIOS.
Only need to press F8 to select non-default OS.
Re-boots are as quick as using traditional Grub-in-MBR option.
Always disconnect other OS's drive if re-installing.
This process will also work for adding Windows to an Ubuntu system
Access to files on either drive can be configured later on, once you've got a safe installation organised.
Edit: The following information will allow dual-booting on two drives with all BIOS versions, with a little editing of Grub. Thanks are due to Anaconda and Bulldog
Yep all good and so, but..
it would be even better if the hd with ubuntu is the master and windows hd is the slave.
Everything would work just like in your example (no grub in windows drives mbr), but you wouldn't have to do anything in the bios, and in all bios:s it propably even isn't possible to select the booting drive..
But if you have ubuntu in master, then when you boot you would go to grub, and you can select which os is booted. The only thing you would have to do is edit /boot/grub/menu.lst and add windows to your grub..
title Windows NT/2000/XP (loader)
map (hd0,0) (hd1,0)
map (hd1,0) (hd0,0)
remapping hd:s when booting to windows from slave drive is nesessary, because windows wants to think it is in the master drive..
and if you remove either hd from your machine, the other one would work normally like in your example...
gn2: The end result is the same, Grub is kept off the Windows MBR.
Bulldog has also made posts advocating this method.
Definitely a very good thing.
GUI Grub Editor Info: http://www.ubuntuforums.org/showthread.php?t=228104.