Why my graphics card shows incorrect 2,5 GT/s or 8,0 GT/s link speed?
Most of NVIDIA cards will show 2,5 GT/s which might look card is working in an outdated PCI-Express 1.1 mode. In reality they use full PCI-Express 2.0 mode, so the reported link speed is just a cosmetic issue under macOS.
Some AMD cards like Radeon RX Vega will also report incorrect 8,0 GT/s speed which is a PCI-Express 3.0 link, while Mac Pro up to 5,1 included only supports PCI-Express 2.0.
Latest AMD cards from RX5000/RX6000 series and W5000/W6000 series won't show GT/s speed at all. You will only see x16 bandwidth width.
To verify you are running a full PCI-Express 2.0 link under Windows just download and install the latest version of GPU-Z: https://www.techpowerup.com/download/techpowerup-gpu-z/
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Bus Interface field shows maximum supported link speed on the left and current link speed on the right. |
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Click question mark symbol next to Bus Interface then click Start Render Test button. |
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You will notice current link speed will increase from PCIe x16 1.1 to PCIe x16 2.0. If you place a cursor on Bus Interface field it will show proper current link speed. |
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If you would like to verify you are running a full PCI-Express 2.0 link under macOS just download and install the latest version of OpenCL Oceanwave & bandwidth Benchmark (supported up to macOS Mojave): https://www.mediafire.com/download/e21738qhs2m9kq3/OpenCL_OceanWave_Bandwidth_V161.zip
You can also use CUDA-Z (supported up to macOS High Sierra): http://cuda-z.sourceforge.net/#block-macosx
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OpenCL OceanWave benchmark won't run correctly, it will be limited by your screen refresh rate, typically 60 Hz, so you will get 60 fps unless you cover the windows e.g. with Safari browser so it can finish benchmarking underneath.
Under Bandwidth Transfer Speeds there are 3 values. The top one is CPU>PCIE>GPU transfer speed and the second one is the reverse. If your card is running at PCI-Express 2.0, these values will both be 4,00 or higher. If your card is running at slower PCI-Express 1.1 speed, these values will be in the 2,00 or 3,00 range. The final number is overall memory bandwidth on your GPU, it is not always accurate. |
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If you have NVIDIA card and CUDA driver installed you can also use CUDA-Z software.
Upon starting the program, choose Performance tab.
If there is a value of 4,500 or above in Host to Device/Device to Host lines then card is running PCI-Express 2.0. If the value is in the 2,500 range then the card is running at slower PCI-Express 1.1 speed. |
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