PCIe (PCI express) graphics card in G4 cube?

[Cktwo]

Hi all,

I know the title sounds nuts, but that's what I am thinking of:

The slot on the logic board that the Cube's AGP/Power daughter board plugs into looks exactly like a PCI slot. But is it a PCI slot? The

If it were a PCI slot, would it be possible to use one of those infamous PCI -> PCIe adapter cards and then use a PCIe graphics card inside the Cube?

I am fully aware that -- if it works at all -- the PCI/AGP bus doesn't get any faster. But the PCIe GPUs internals, memory etc. are way faster than any PCI graphics card. And since the very last G5 PowerMacs were equipped with PCIe slots, MacOS X *should* support some (old) PCIe graphics cards, shouldn't it?

This is the G4s AGP/Power daughter board as you all know it:


And this is one of the PCI -> PCIe adapter cards (bottom PCI, top PCIe):


What do you guys think?

Cheers
CK

 

[Powerbase]

I swear I was reading about someone doing something along this lines a little while ago in a G5 or something I can't seem to find the article or post, though.

I don't think that's a PCI slot in the Cube, though. Just because it looks the same DOESN't mean it is. You're probably out of luck on that one.

EDIT: Here it is

 

[joevt]

The daughter board appears to have the same number of pins as the PCI adapter except the PCI adapter replaces two pins with a notch.
That means the PCI adapter could fit but I would check the continuity of all the pins of the AGP slot to make sure the daughter board pins have the same function as a PCI slot.


The PCI adapter is keyed for 3.3V and 5V.
The AGP slot appears to be 1.5V?
If the G4 requires 1.5V then an adapter would need level shifters?

There might be too many other differences:
https://www.cs.umd.edu/users/meesh/cmsc411/website/projects/agp/pci_vs_agp.htm
https://en.wikipedia.org/wiki/Accelerated_Graphics_Port
https://en.wikipedia.org/wiki/Peripheral_Component_Interconnect

The wiki page says:
"An AGP bus is a superset of a 66 MHz conventional PCI bus and, immediately after reset, follows the same protocol. The card must act as a PCI target, and optionally may act as a PCI master. (AGP 2.0 added a "fast writes" extension which allows PCI writes from the motherboard to the card to transfer data at higher speed.)"

You probably need a AGP to PCIe bridge. I don't think they exist outside of some AGP cards that used a PCIe GPU. Alternatively, you could get a AGP to PCI adapter. Then connect a PCI to PCIe bridge.
https://www.vogons.org/viewtopic.php?t=78627
https://www.vogons.org/viewtopic.php?f=63&t=76665

 

[Byrd]

It's not electrically compatible with PCI - note the riser card does other functions, get ready to lose your Cube if you plug this adapter in.

Even if it did work you are starving the card off the PCI bus and you would be very limited in what card you could use considering space, thermals and power.

 

[François]

And the AGP bus is non standard on Macs with an ADC port for video: it carries USB data lines. (That’s why you have to tape or cut two pins on a PC card flashed for Mac)

 

[Nixontheknight]

And the AGP bus is non standard on Macs with an ADC port for video: it carries USB data lines. (That’s why you have to tape or cut two pins on a PC card flashed for Mac)

or just on the adapter itself

 

[Powerbase]

And the AGP bus is non standard on Macs with an ADC port for video: it carries USB data lines. (That’s why you have to tape or cut two pins on a PC card flashed for Mac)

Apple used some pins for their adc stuff that were originally unassigned on the AGP connector. They were used on 8x AGP which is why you have to tape em off.

 

[Cktwo]

I didn't dare plugging it in yet since I don't want to destroy my Cube. But still, being able to use a PCIe GPU in a Cube would be cool, wouldn't it? I know that the speed increase wouldn't be huge. So why? Because we can (maybe)!

 

[Powerbase]

It's be interesting, but you'd have more luck trying to get an adapter for AGP to PCIe. From what I'm seeing they were vaporware (I just did a quick search, though).

That's if MacOS would even know what to do with a AGP to PCIe adapter or a newer-than-it-or-drivers PCIe video card that you plugged in.

Edit: Oooo, I found this. So, in theory, if you found the pin out of that pci-like to AGP adapter you could probably make an adapter that fits in there, maybe