I dug out an old Macintosh Quadra 800 that I've had on my shelf for a long while. I'm not even sure where I got it anymore... After a quick look in my VGA adapter bucket, I found I had the needed 15pin to VGA adapter, so I decided to fire the machine up and see if it still works.
My first attempt was met with absolute failure as it was very clear the machine wasn't doing anything. No power supply fans, or beeps... just... nothing.
So, I popped the hood and discovered that someone had been there before me, as the HDD was missing and the power to the motherboard was unplugged.
I re-attached motherboard power, and tried my experiment again. This time, I was able to get video and have an (expected) icon of a floppy disk with a little question mark. Obviously the mac has no HD, so it's looking for something to boot from.
Newer models can boot the OS from CD-ROM by holding the Option key, or Ctrl-C, or something like that... but I wonder, is a vintage Quadra able to perform a similar trick?
I do not have any vintage Mac floppies, and no hardware currently capable of downloading and/or creating a bootable vintage floppy. What I do have is a single original System 7.6.1 CD-ROM, which I thought might boot. But after a few google searches and some random experimenting I haven't had any success.
Does anyone know if it is possible to boot a quadra from CD, and if so, what the procedure is?
About 5 minutes after posting this question, I went back and took a closer look at the machine and discovered that whoever had the machine before me had disconnected everything from the motherboard, not just the power. The Quadra has a really funky mounting mechanism for the motherboard, but after some jiggery-pokery I reattached the floppy/cd/speaker cables and tried again.
This time, in the absence of the HDD the computer automatically fell back to the CD-ROM drive and booted 7.6.1 from CD without any hotkeys required.
However, I am leaving the question open in the hope that someone knows if a key combination is available for the Quadra to boot from CD when the HDD is installed.