These are not my notes. They helped me get sorted out though. I just use the early boot menu to select the partition I want to boot from.
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In sys:kickstart/kicklayout search for BootDevice. Remove the ";" at the beginning. Then in a shell type echo > kickstart/BootDevice "dh1" where dh1 is the OS4 boot partition
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My solution to dual booting OS3.x/OS4 is as follows:
1) You need seperate partitions for each OS, I'll call them OS3: and OS4: for this tutorial
2) Give OS3: the highest boot priority
3) Edit OS4:Kickstart/KickLayout-WhicheverAmigaYouHave and uncomment the "MODULE Kickstart/BootDevice" line
4) From a shell type "echo > OS4:Kickstart/BootDevice "OS4"
5) Copy the Kickstart directory from OS4: to OS3:
6) Copy Bootloader from OS4:C to OS3:C
Substitute the partition names as appropriate. In step 3, choose the Kicklayout file that matches your Amiga model.
Now when you boot from the OS3: partition, you can run Bootloader (from shell, Opus button bank etc.) to load the OS4 kickstart files and autoboot the OS4 partition. In OS4, run C:Reboot to reset to KS3.x. You can still go straight to OS4 by selecting its partiton in Early Startup Control.
This method can be used with boot utilities such as SelectOS from Aminet, or start OS4 from the OS3.x Startup-Sequence if a mouse button is held down etc.
