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    USB 2 Speed vs USB 2 Devices in USB 3 Ports

    Discussion in 'Hardware Components and Aftermarket Upgrades' started by decworld, Jan 25, 2012.

  1. decworld

    decworld Notebook Evangelist

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    Hi,

    Really confused by some speed tests done today using an external gigbit ethernet adaptor.

    When connected to a USB 2 port I get

    25MB/s transfer speed, using around 20% of bandwidth as shown by task manager

    When I connect the same device to a USB 3 port (the device is USB 2 only) I get

    35MB/s transfer speed, using around 30% of bandwidth.

    This takes a 64 second transfer down to 45 seconds. But its still a USB2 port.

    Any ideas anyone.

    PS, I ran the USB through a power hub both 2 and 3 with the same results.

    Thanks,
    Dec
     
    decworld, Jan 25, 2012
    #1
  2. Commander Wolf

    Commander Wolf can i haz broadwell?

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    What exactly is the problem here? You are bottlenecked by the device's USB 2 interface... even though it's nominally a "gigabit" device, you're never going to get gigabit speeds as USB 2 can't handle more than 25 to 35MB/s.

    Device manager is giving you a figure based on the theoretical gigabit limit... it doesn't know that your dongle is capped by USB 2.
     
    Commander Wolf, Jan 25, 2012
    #2
  3. decworld

    decworld Notebook Evangelist

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    Hi,

    thats understood, but not my point.

    My question is why is one usb port faster than the other ?

    Thanks
    Dec
     
    decworld, Jan 25, 2012
    #3
  4. decworld

    decworld Notebook Evangelist

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    SO I now have a theory.

    USB 3 hub is on a bus with no other devices.

    The USB 2 hub bus is shared with the bluetooth/webcam/card reader and each reserves a small amount of bandwidth should those services need to function.
     
    decworld, Jan 27, 2012
    #4
  5. kent1146

    kent1146 Notebook Prophet

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    There are several possible reasons for why you get 25MBps vs 35MBps.

    * Not all USB controllers are created equal. Some may have higher latency or overhead than others

    * Not all USB controllers are connected to motherboard resources the same way. Some implementations may create higher latency or overhead than others



    * It is possible that your testing environment is imperfect. We don't know enough about the scenario you are using to test, to be able to tell you whether your test scenario is appropriate.

    If you are doing a copy of multiple small files to a mechanical HDD or from a mechanical HDD, then you are are going to be bottlenecked by the random read/write speeds of the source/destination drive.

    If you are copying the same file(s) to the same location(s), then it is possible that there is some kind of caching that is taking place, rather than true disk-to-disk read/writes over the network
     
    kent1146, Jan 27, 2012
    #5