mac graphics cards had their own rom so you cant put a PC graphics card one in, unless you can flash the mac rom into them.

Well, here is a post you may find interesting:
This is not a PC, but it may as well be! (My PowerMac G3 Blue & White)

lmttn wrote on 2026-06-26, 02:43:

Hello, I have a 1999 Power Mac G4 (graphite model, 400 MHz) coming in soon and I have two small questions about it: […]
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Hello, I have a 1999 Power Mac G4 (graphite model, 400 MHz) coming in soon and I have two small questions about it:

• What PCI graphics cards can be used as upgrades over the included ATi Rage 128?
• Can I use any old USB 2.0 PCI card and PC100 SDRAM or is it picky about either of these things?

Maybe. Mac OS X can use NEC and Ali card without drivers. If you have a Via chips on the card... change the card

The upgrades depend on whether Mac OS 9.x or OS X is the OS of choice.

If it's an G4 Yikes with a PCI graphics card, then the PC bus slot is running at 66 MHz. It's like AGP, without GART etc.

The original ATI card probably runs at 66 MHz, while PC cards run at 33 MHz.

Speaking in general, most OS 9 hardware also works on X.
But there are some special cases and a few limits.

A Geforce 2 or Geforce 4 MX can be flashed rather easily, for example.
Many versions have an ordinary EPROM chip in a socket.
The standard timings usually work, though there are tweaking utilities.
Also, it's always good to backup the original EPROM.

For OpenGL 2 compatibility, an Geforce FX 5200 can be used.
But it has no 3D drivers for Mac OS 9 anymore.

Speaking of Quartz Extreme and Mac OS X 10.4 Tiger, there's a workaround to enable it for PCI graphics cards.

Are you sure this is a PCI model? It may be an AGP model; both were available as 400 MHz. You may wish to check that before picking up a video card upgrade.

Yeah, this is the PCI model. I got it in yesterday to learn that I have several things to replace in it (hard drive, RAM, OS 9) but the graphics card does work fine. Honestly if it plays Myth II without issue (which I'm sure it does) then I will likely never feel the need to upgrade.

Okay, followup questions now that I'm sure the system is doing everything in its power not to boot. It did boot to a very slow and bloated OS 9.0 installation at first, but now it exclusively gives me the question mark folder message at startup. Even with a disc in the drive, none of the key commands for startup seem to be doing anything. Is it because I am using a PC keyboard instead of a Mac keyboard? The HDD and CD-ROM drives are audible, and the CD-ROM drive's access light works and shows that it's trying to at least do something. This is a "Yikes!" model G4 which according to a Reddit post is missing the later Macs' boot menus.

As a vintage Apple fanboy, can I suggest keeping your machine on OS9? It'll run very nicely and games for OS9 will be blazing fast. OSX will feel a bit more sluggish...actually a lot more sluggish 🤣. Or maybe keep an OS9 and OSX partition? If you want to run OSX, finding a mac mini g4 is super cheap and will give a better experience.

The plan was always to stay on OS 9. I learned the hard way in elementary/middle school just how dismal OS X can be on old PPCs.

Not to derail but there's a project to run OS9 on Apple hardware that was never truly supported. I ran OS9 on my Mac Mini and had a much better time than OSX!

There's a guy on a mac forum that sells CPU accelerators. Let me know if you're interested and I can try to track him down. They're not cheap, though.

Those accelerator and compatibility cards do look very cool, but first I'd need to get this thing to even boot into an OS at all.