Can someone help me understand my MacBook Pro PCIe interface please?
 
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[Solved] Can someone help me understand my MacBook Pro PCIe interface please?  

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Luke Perman
(@luke-perman)
New Member
Joined: 1 year ago
 

Hi there - I've had a good search but can't find the explicit information I'm looking for.

I'm running a Razer Core X with an NVIDIA 2070 SUPER GPU, on a MacBook Pro 2019 in Windows 10.

I have the Razer Core X plugged into one of the left hand ports as they report as being "PCIe Controller (x8)" ports in Windows device manager.

However, when I check my PCIe port bandwidth usage in GPU-Z (with a render test) it reports that the port is running at max PCI-Express x4 3.0.

I don't understand why it isn't using the whole x8 as I don't have any other devices connected to the other port on that side.

I also have an Oculus Rift S that I am plugging into one of the right hand side ports that come up labelled "PCIe Controller (x4)".

Everything works OK although I am a little disappointed with the overall Rift S performance, but unclear on whether my PCIe port usage has anything to do with it or not.

Thanks in advance for any pointers - I'm mostly just trying to understand the labeling of the PCIe interface in windows device manager and whether this has any correlation to expected bus speeds.

PCIe bus interfaces

Apple Mac Mini (Late 2014), i7-4578U @ 3.0hz, 16GB RAM
Akitio Thunder2 with Inno3D Herculez X1 GTX 970


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Luke Perman
(@luke-perman)
New Member
Joined: 1 year ago
 

I'm an idiot. Let's just leave it at that 😀

Ok, just FYI ... the reason it's only showing as PCIe x4 is because of the Thunderbolt 3 connection is only as fast as PCIe x4:

https://developer.apple.com/documentation/metal/gpu_selection_in_macos/understanding_gpu_bandwidth

Nice to see such a detailed article from Apple. It took quite a bit of googling to find that 🙂

Apple Mac Mini (Late 2014), i7-4578U @ 3.0hz, 16GB RAM
Akitio Thunder2 with Inno3D Herculez X1 GTX 970


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DeliciousAlbatross7
(@deliciousalbatross7)
Active Member
Joined: 6 months ago
 

Thunderbolt 3 supports only 4 lanes of PCI-e, that is why GPU-Z is showing x4. 

2019 16" MacBook Pro (RP5500M) [9th,8C,H] + RX 5700 XT @ 32Gbps-TB3 (Razer Core X Chroma) + macOS 10.15.5 & Win10 1903 [build link]  

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Luke Perman
(@luke-perman)
New Member
Joined: 1 year ago
 

@deliciousalbatross7, yeah I just discovered that a couple of minutes ago 🙂

 Thanks.

This post was modified 2 weeks ago

Apple Mac Mini (Late 2014), i7-4578U @ 3.0hz, 16GB RAM
Akitio Thunder2 with Inno3D Herculez X1 GTX 970


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