Adding PCIe (Yes, PCI-Express) to your AGP/PCI-Based PowerPC Mac

The Peripheral Component Interconnect Express, aka PCIe, is a longstanding serial computer expansion bus standard created in 2003. The Late 2005 Power Mac G5 was the only PowerPC Mac which took advantage of this technology, which had a production run of October 2005 – August 2006. As a result, AGP/PCI-based Macs received 1-2 years lesser of hardware support, whilst simultaneously being left behind just like the short lived Late 2005 Power Mac G5. Now, it’s possible to use PCIe devices on an AGP/PCI-based Mac, with an adapter card. As of the time of writing this article in late September 2023, this adapter seems to be known by some in the computer enthusiast community, but is seldom if at all documented.

Note: This article is a mashup of initial findings, with limited available devices to test with. A later article may be published highlighting device compatibility.

Your eyes aren’t playing tricks on you, this is precisely what it sounds like. We’re talking about straight up adding a PCIe slot interface to your AGP or PCI-based PowerPC Mac. It is entirely possible to add PCIe to a computer such as a Power Macintosh G3 B&W, for example, it’s been done. The question, however, is down to software support, and OS version.

Pictured below: The adapter in question adapts a PCI slot interface to a PCIe slot, allowing a single PCI slot to connect a more modern PCIe device.



Motive behind the project

Although I personally have only stumbled into such an adapter recently, some on the LEM Facebook community have had experience with it. This adapter allows PowerPC Macs of an earlier era to take advantage of the very final generation of hardware upgrades available for PPC, and some change. Due to the nature of “PowerPC + PCIe” Macs being of a newer generation, it’s highly likely only Mac OS X Tiger and Leopard are going to be able to properly take advantage of any PCIe devices. As of right now, I don’t have all the devices I’d like to test via PCIe, but it’s enough to get started on the concept of turning this fun project into something more practical. The Pandora’s box is open.



Devices tested in this initial run

  • Mac Nvidia GeForce 6600 LE (PowerPC)
  • OWC Accelsior Mercury SSD
  • ATI Radeon 2600 HD 256 MB (Intel, 64-Bit EFI)
  • Mac ATI Radeon X1900XT (Intel, 32-Bit EFI)
  • Gigabyte Titan Ridge

P.S. Neither intel card works in a PowerPC Mac.

OWC Mercury Accelsior 480GB SSD

The first round of testing wound up to be nearly a success. It’s a bummer you can’t boot off this OWC drive specifically, although I’m not going to speak for regular SATA PCIe SSD based cards overall, based off this test. This 480GB OWC SSD shows up A-ok in both the Power Mac G4, and the Power Mac G5. Holding down the option key to view the drive in either the G4 or G5 upon booting does nothing, it’s strictly viewable in the OS as a storage solution. For those with unfilled/unused PCI-X slots that also have no other way of adding storage, this may work for you. There are cheaper options too, such as Sata 3.0 2.5″ SSD PCIe cards.


Nvidia GeForce 6600 LE – Power Mac G5

Things still seemed normal with the G5, not so much on the G4. I wonder, however, why this is the case (More on this later on in the article). In the case of the G5, this was as straightforward as you can be. You just plug, play, and everything works. I’m willing to bet every card that works in a PCIe G5 also works in an AGP G5. Cards which require additional 6 or 8-pin power cannot be left unplugged at all, the PCI bus will only supply 25W to the card in total.

There’s really nothing to write home about in regards to the performance or functionality of a PCIe GPU on an AGP G5 as it is. It seems pretty straightforward, minus how it’d be mounted inside a computer. Perhaps, it’s worth looking into specific performance metrics down the road, however, it it can be inferred that even a better performing PCIe GPU plugged into a PCI slot wouldn’t perform as well as an OEM or flashed GPU in an AGP slot. The point of having such a thing is more so.. longevity, additional monitors, or for fun. Having a PCI GPU becomes troublesome when other devices are also plugged into other PCI slots, the parallel/shared bandwidth goes way down. In the case of the G4, having all of the regular peripherals plugged in resulted in a noticeably laggier redraw rate in those initial startup screens. No thank you!


Nvidia GeForce 6600 LE – Power Mac G4

Unfortunately, this one isn’t good news. This card will not work past the Apple logo in Sorbet Leopard, but take this with a grain of salt. A LEM Facebook user submitted a screenshot of their B&W running a Quadro FX 4500, so it seems the hardware configurations can play differently depending on what’s plugged together. In the case of this project, this was a no go. It’ll even let me pick a volume to boot into, but won’t boot into a volume itself.

Above: Right there is where the 6600 LE hangs in Sorbet Leopard in an AGP Graphics Power Mac G4.

Below: A user screenshot demonstrating a Quadro FX 4500 running on a B&W G3. The computer is named as a Power Mac G4 however is shown as a PowerMac1,1 in system profiler.


What else works?

There’s a good possibility many other devices work in the range of what’s been tested and approved to work in MacOS and with other PCIe PowerPC Macs. Storage devices and some BT/Wifi cards are likely to be the furthest reaching chronologically (to present), it may even be possible somehow to adapt a Mac Pro 4,1 BT/Wifi card to work in a PowerPC Mac. Who knows? This article reflects on a short period of time spent on a few devices across 2 different Macs, and is a proverbial “Pandora’s box is now open, what now?”. I would love to test more devices out with this, but that will come with time. The reality is, however, this is yet another way to prolong our Macs!

Pictured below: An Intel ATI Radeon HD 2600 plugged into a Power Mac G4.