Hey thanks for the response.
You're right, they're not identical. IDH0 has something called AsimCDFS on it, IDH1 does not. When I boot normally I briefly see a message that says "Mounting AsimCDFS..." so it must be booting from IDH0. If I boot with the mouse buttons held down, I can choose from DF0, IDH0, IDH1, and DF2. Choosing IDH1 results in the animated "insert floppy" screen.
The WBStartup drawer on IDH0 has another drawer inside called WBStartup-disabled. IDH1 does not.
That's confusing, if IDH0 is the boot partition. (?)
Asimcdfs is a cdrom filesystem. i guess it has a cdrom drive in the 4000?
IDH0 sounds like the main boot drive,the other may of been a basic workbench back up or ...who knows..you get the boot screen because IDH1: is not bootable.

mech