HP-UX

To interrupt boot process in HP-UX, you press the space-bar...
Since its old HW I suppose you would have a double beep sound or on display you should see the keyboard loading... at that instant you interrupt, but do you know what to do next?
There is no need to look at the boot ROM to see what HP-UX you are running, just type uname -r ( or -a to have it all...)
If you have two same disks you can use dd to make an "image" of the first...
You can also use mkrs on a disk device

---------- Post updated at 16:46 ---------- Previous update was at 16:18 ----------

Could this be of any help?
Survival Guide for Apollo Workstations

It turns out that the technicians burnt up the 16-track tape we had that was like a Win98 startup floppy to get to DOS-like command prompt. The old tape drive burnt it up last time they attempted a load a month ago. Now we have to find a way to do that too.

The main issue here seems to be about how to get a root prompt.
Has the application been identified?

Look at :
HP Computer Museum
Read carefully the collector's notes (for there is maybe something you can check and perhaps rescue...).
I am sure you can use a DAT DDS1 external drive (I had one for my 9000/712 running 9.0) so it may be a solution other than finding a same disk and cloning using dd command

That certainly is now a problem I did not know about. I thought I would be able to get to the prompt with the space bar trick, but came to find out the tape doesnt work anymore. Now I need to locate or be able to make a bootable tape from the one controller that is working if I can get into the OS maybe I can do that.