TB3/USB-C port/hub math

Discussion in 'MacBook Pro' started by olliebojangles, Nov 12, 2016.

  1. olliebojangles macrumors newbie


    Oct 30, 2016
    So I have a question, and please bare with me on this, but it related to the 4xTB3 ports on the new 2016 rMBP (15in version).

    We all know that TB3 is used in conjunction with the USB-C port design, and there are plenty of examples of dongles and hubs, but what is the limiting factor on these? If USB3 is ~5Gbps, USB3.1 is ~10Gbps, and TB3 is ~40Gbps, then how many devices can be powered through a single TB3/USB-C port? Is it basic math (4xUSB3.1 devices using one hub equals ~40Gbps which equals the speed of one port)? Or is it more complex than that?

    I'm sure people have asked the question, but in my scenario, I have 10 external hard drives of various sizes and years, all running a variety of USB2,3,3.1 along with monitors and other devices. Now I'm sure I can just go ahead and buy multiple docks if I wanted to, but how much can I plug into one port before I start to lose bandwidth?


    This dock by Belkin for example has many ports in their hub:

    1. Gigabit Ethernet
    2. Audio Out
    3. 2x USB-A 3.0
    4. 2x Thunderbolt 3 (USB-C)
    5. DisplayPort
    6. Power
    7. Connection Status
    8. USB-A 3.0
    9. Audio Out)

    Wouldn't using all of these at once limit the speeds on each? And if not, can you daisy chain more hubs using the 2xTB3 ports?
  2. zhenya macrumors 603


    Jan 6, 2005
    In practice you aren't going to run out of bandwidth with any of those devices on a single Thunderbolt 3 port. Most external drives, assuming they are not SSD, are going to top out at about 1Gbps each, so even connecting all 10 of them and you've barely exhausted 1/4 of the available bandwidth (Assuming you had some way to write to them all at maximum speed at the same time). More likely you'll run out of power for them on most basic hubs before you run out of bandwidth.
  3. MareLuce macrumors 6502a

    Sep 26, 2010
    Great question; thanks for asking it!

    With my current USB ports I'm usually either using all of them or none of them.
    all of them =
    - charging 2 phones, 1 iPhone, 1 Android, and a bluetooth earpiece
    - plugging in 2 external WD My Passport Ultra drives
  4. olliebojangles thread starter macrumors newbie


    Oct 30, 2016
    zhenya, thanks for that info.

    I just haven't heard anyone talking about how much each TB3 port can handle (as Apple's dongles are 1 for 1 converters).

    So if I'm reading that correctly, I should have no problem finding or daisy chaining hubs together to support external hard drives (each with their own power source) all through 1 of my 4 TB3 ports? Really goes to show that this change is so much better than many people realize (yeah dongles/hubs can be a pain, but the MBP can really support so much more now!)

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