The motherboard photos I find do all show universal AGP with SiS 645, and so does the Playtool AGP site:
http://www.playtool.com/pages/agpcompat/agp.html

I have a P4S5A packed away somewhere. I don't have any Voodoo cards, but I do have some old ATI Rage cards that I guess require 3.3v. Do you just need to find out if it will POST without blowing up? Or is it more involved than that?

shamino wrote:

I have a P4S5A packed away somewhere. I don't have any Voodoo cards, but I do have some old ATI Rage cards that I guess require 3.3v. Do you just need to find out if it will POST without blowing up? Or is it more involved than that?

Pretty sure see if it posts.

Thank you for your interest in this.

The m/b has a universal-looking slot so most probably it works as such too, just wanted to make sure that this is really the case. I know it's not that common, but while working as a technician back then I've seen this happening more than once with m/b's of that era having an unkeyd agp slot and never working with any 3.3V card.

@shamino: that would be really helpful. If you could just power it up for a few moments and see if it can post with a 3.3V-only keyed card... Chances of damaging the card with less voltage are minimal, but it's something I'm not doing with a voodoo 😀

It seems to work fine.

I tried 2 cards, first a Matrox G2+ (disposable) and then a 3DLabs Permedia (why not - I was already convinced by this point. 😀 ). I thought the latter card was a Permedia2, but the POST just says Permedia... anyway the copyright is 1997, whatever it is.
Both are AGP cards keyed for 3.3v only. They both POSTed and went into the BIOS setup without any issue. I didn't measure the AGP voltage and it isn't reported in the BIOS, but given their age I assume these cards truly require 3.3v, so it looks like 3.3v support works fine in the P4S5A.

After reading your reply I tried my card which also works OK. Thank you thank you thank you for your time!