I take all your points zrb and thanks.
After it’s booted any of the three machines have run flawlessly. Indeed one of them is connected to an AJA IO via FW (another bus) No problems capture/edit uncompressed 10 bit SD. Media is on a 320 SCSI.
To answer your question, I’ve always just waited (and sometimes waited and waited!) for the Mac to find the FW OS drive. This is really the issue, not being a Mac man I wondered if there was something I could do to help the machine find the drive.
I have set the startup disc in system prefs.
I didn’t know about the option of alt key on bootup. Presumably this is for situations where there is a choice of OS. I’m not with my Mac at present but will give that a go.
Thank you for your ongoing support
Alan