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USB bottlenecks - what are they?

  • 08-09-2009 8:18pm
    #1
    workaccount
    Closed Accounts Posts: 2,460 ✭✭✭


    Hello,
    Just looking up the specs of the new USB 3 here at the moment and comparing them to USB 2.

    Firstly the max rate of transfer for USB2 is 480mbps. This translates to 60 megabytes per second. I don't think I've achieved this kind of speed ever. Have I done my calculations wrong or where are the bottlenecks?

    So on to USB 3 then which has a speed of 4.8Gbps. That's translates to 600 megabytes per second. Sounds cool - I can understand how Amdahl's Law is applicable here.

    Technology is similar to PCI express - maybe a card will be available to upgrade desktops.


Comments

  • #2
    AlmightyCushion
    Moderators, Education Moderators, Technology & Internet Moderators Posts: 35,109 Mod ✭✭✭✭AlmightyCushion


    The bottleneck is the thing you are transferring to. USB memory sticks usually have crap transfer rates especially really cheap ones. Also with usb you the max speed is the burst speed. It will do that transfer rate for a short while and then drop to a slower speed.


  • #3
    Bob_Harris
    Closed Accounts Posts: 1,619 ✭✭✭Bob_Harris


    Your typical "fast" USB pen drive these days will be advertised as something like 17/32MB write/read. Older ones will have far lower numbers.

    Some of the faster ones have a write and read speed of roughly 35MB/s

    (MB as in MegaBytes)

    The actual rate will probably be less, you can check it out with this. Start the app, click on your device to highlight it, then Ctrl+T to start a speed test.

    USB also has a fair bit of overhead (as in control, data packet headers etc).


  • #4
    Overheal
    Registered Users, Registered Users 2 Posts: 85,927 ✭✭✭✭Overheal


    even with external drives like WD passports youre only talking about - on a very good day - 15, maybe 20 MB per second.


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