1

On a 2008 Mac Pro (a.k.a. MacPro3,1), it apparently has 2 PCIe 2.0 slots and 2 PCIe 1.1 slots. While the difference won't prevent any PCIe device from working, it does make a difference for speed.

I recently ran GPU-Z under Windows 7 and ran the load test (a '?' icon off to the right next to text about PCIe versions and number of lanes) and found that it stayed at PCIe 1.1 x16. This is with a Radeon HD 270X which is definitely PCIe 3.0 compatible, so I'm a bit surprised it didn't report 2.0!

Trying to look at Intel 5400 chipset documentation, it would seem that the chipset only supports PCIe 1.0/1.1, but all documentation on the MacPro3,1 that I've seen suggests that the first two slots support PCIe 2.0 (which I presume is direct into the CPU rather than the northbridge).

Any confirmation on the spec here? As well, why would GPU-Z only be reporting PCIe 1.1? Could it have something to do with the fact that I have a USB 3.0 card in slot 4?

2

If that is a PC (non-EFI) graphics card, running it in Windows on a Mac (Bootcamp) will reduce the speed to PCIE 1.1

You must have an EFI flashed card to run at PCIE 2.0 in Windows on Mac machines. Drivers solve this issue for some PC (non-EFI) cards in OS X, but not Windows.

Real world gaming difference between 2.0 and 1.1 will likely be negligible, and your bottleneck will most likely end up at the CPU or OS X drivers. Generally I see better performance in Windows.

For reference I run a GTX 1060 (non-EFI) on a 2009 Mac Pro; my benchmarks and real world gaming are all better in Windows, at the PCIE 1.1 speeds.

  • Yeah, I think this is the ticket. After posting this question I did find on some other forums information about cutting resistors or some hack for other Radeon boards to get PCI 2.0 speeds. It seems that if it doesn't recognize the card as a Mac EFI one, then it throttles it. grrrr :-) – bjb Oct 24 '17 at 16:55
0

Obviously I can only comment on how you've described things in your question, but the results you describe don't quite make sense to me.

This model Mac Pro does indeed have two PCI Express 2.0 slots and two PCI Express 1.1 slots. However, while the two PCI Express 2.0 slots are x16, the two PCI Express 1.1 slots are x4. So, getting a result of PCIe 1.1 x16 really isn't right. In other words, the x16 would indicate PCIe 2.0, not PCIe 1.1 that is only x4.

By default one of the PCIe 2.0 x16 slots was occupied by the GPU, which presumably is where you also have your Radeon HD 270X installed. But if you had it installed in one of the PCIe 1.1 slots, then it should be reporting PCIe 1.1 x4.

In a nusthell, GPU-Z reporting back PCIe 1.1 x16 makes no sense.

0

Looking at the Official Apple Technical Specifications page, it says the following re: PCI expansion

PCI Express expansion7

  • Three open full-length PCI Express expansion slots
    • One PCI Express 2.0 x16 slot
    • Two PCI Express x4 slots

So, according to Apple, the x16 slot is PCIe 2.0

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .