Tips on using Thunderbolt devices with the 2013 Mac Pro

The 2013 Mac Pro has six (6) Thunderbolt 2 ports that you can use. Below are some useful tips to know.


Choosing the right Thunderbolt port / BUS

The 2013 Mac Pro has six Thunderbolt ports but "only" 3 busses, which are as follows:


© Apple Inc.


You should connect devices that use a lot of bandwidth on different Thunderbolt busses. Also if you are using the built-in HDMI output, prefer to use busses 1 & 2 as the built-in HDMI output is also on Thunderbolt Bus 0.


Recommended configuration for the M|Family

The M|80, M|62 and M|44 use a lot of bandwidth, so you should connect your M|Family device alone on one BUS, he should not share the bandwidth with another device. See the diagram below of one recommendation.


Of course, this is one possible configuration, and you could connect the M|family device on BUS 1 and your storage on BUS 2, that would make no difference. But avoid BUS 0 that can share the bandwidth with the Display.


Number of channels that can be done on one BUS

As said earlier, the number of channels that can be achieved can differ considering multiple factors, and what other devices are running on the same Thunderbolt bus. Below are a few things to consider.

The Mac Pro 2013 uses Thunderbolt 2, so are the M|Family devices. Here are the limitations for one Thunderbolt 2 BUS:

  • 8 bit
    • 1080i29.97 (or 720p59.94): Max 8 channels (in or out)
    • 1080i25 (or 720p50): Max 8 channels (in or out)
  • 10 bit
    • 1080i29.97 (or 720p59.94): Max 7 channels (in or out)
    • 1080i25 (or 720p50): Max 8 channels (in or out)

Note that if you use a different device that still uses Thunderbolt 1, you will have half the bandwidth that you can achieve with Thunderbolt 2 (max 5 channels in 1080i29.97).


What happens if you reach the limit ?

There will be 2 consequences:

  • In the Activity and Logs window, you will see a log saying: "Video Card buffer underrun". This is because we can not get the frames quick enough from the video card.
  • As we can't retrieve the frames quick enough from the video card, we will duplicate the corresponding video frames and drop audio, so there will be drops in both audio and video in the recorded file.
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