Resolved USB 3 device in USB 2 device not running at full speed?

Discussion in 'Mac Accessories' started by poiihy, Dec 31, 2014.

  1. poiihy, Dec 31, 2014
    Last edited: Jan 2, 2015

    poiihy macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #1
    I have USB 3 external hard disk. When connected to a Mac with USB 3 port, the hard disk runs at speeds ~100MB/s of Read and Write. But on my older MBP with only USB 2 ports, it only runs at ~30MB/s R/W. The Maximum speed of USB 2 is 60MB/s, so why is it running only half?
     
  2. ColdCase macrumors 68030

    Joined:
    Feb 10, 2008
    Location:
    NH
    #2
    USB3 is by directional, USB2 is simplex... USB3 protocol is more efficient when storage handling data.... bunch of things including the old MBP hardware.
     
  3. poiihy thread starter macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #3
    USB 3 device connected to USB 2 host should run the same as a USB 2 device connected to USB 2 host.

    I'm just wondering why it runs at only half the maximum speed.
     
  4. takeshi74 macrumors 601

    Joined:
    Feb 9, 2011
    #4
    Your answer lies in the comment above that USB3 is full duplex (referred to as bidirectional above) while USB2 is not. It is running full speed.
     
  5. poiihy thread starter macrumors 68020

    poiihy

    Joined:
    Aug 22, 2014
    #5
    You mean USB 3 devices are full duplex and USB 2 devices are not, so native USB 2.0 devices will be able to run at 60MB/s but native USB 3.0 devices won't?!

    I thought USB 3 has the same connectors as USB 2, just an extra 5 pins. SHouldn't it function exactly like a USB 2 device when used as a USB 2 device?
     
  6. waw74 macrumors 68030

    Joined:
    May 27, 2008
    #6
    that's about what i expect from a USB2 drive.
    the 60 is the "theoretical maximum"


    link
     
  7. matreya macrumors 65816

    matreya

    Joined:
    Nov 14, 2009
    #7
    Jesus, it's like trying to program a potato to do aerobics...

    Just accept that USB2 drives (and USB3 drives that are operating on a USB2 bus) will never exceed 30MB/sec

    The fact is your Mac is old and out of date :)
     
  8. ColdCase macrumors 68030

    Joined:
    Feb 10, 2008
    Location:
    NH
    #8
    You have a USB2 drive that operates at 60MBPs?
     

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