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Thread: Meaning of USB 2.0 backward compatibility

  1. #1

    Smile Meaning of USB 2.0 backward compatibility

    Hello,

    USB 2.0 is said to be "backward compatible" with USB 1.1
    In my humble understanding (or lack of it), there are 3 participants in any USB usage scenario. The PC, the cable, and the device. Considering that there are these 3 participants, many questions arise in my mind as to what exactly this "backward compatibility" means. For example:

    (1) Between USB1.1 and USB2.0, is there any difference in the connecting cable, or does the difference lie entirely in the PC and the device that are connected by the cable?
    (2) If my PC is USB is version 2.0, my cable is USB1.1, and my device is USB2.0, will these 3 participants work together? If they will work together, will I get USB2.0 speeds or will I get USB1.1 speeds?
    (2) If my PC is USB1.1, but my cable is USB2.0, and my device is USB1.1, will these 3 participants work together? If they will work together, I suppose I will get USB1.1 speeds. Right?

    My problem at the moment:
    I wish to purchase a PC-to-PC USB file transfer kit. The kit consists of a USB-based cable, and some Windows-explorer-like software for file transfer. Kits currently sold in the market offer only USB1.1 speeds, so I'm mulling the following questions:
    (a) If I buy this kit, will it work in future with a USB2.0 PC's? If Yes, will I get USB2.0 speeds or not?
    (b) If I wait long enough, will there be such a thing as a USB2.0 file transfer kit?

    thanks,
    chaith

  2. #2
    Join Date
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    Post

    A google search turned up alot of reading http://www.google.com/

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  3. #3
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    The backwards compatibility means that you can plug a USB 1.1 device into a USB 2.0 port and it will work.

    There are cables marketed as USB 2.0 cables, so there may be a difference between old and new USB cables. If so, using a 1.1 cable would most likely limit you to 1.1 speeds. 2.0 cables will work with both 1.1 and 2.0. However, you only get the faster speed if the ports are USB 2.0

    I'm sure it's only a matter of time before 2.0 transfer kits show up on the market, but if you used the software that came with the 1.1 kit for two pcs that have USB 2.0 and you had a USB 2.0 cable, it would most likely work at the faster USB 2.0 speed.

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    When all else fails, read the instructions.

    Microsoft Knowledge Base

    Drivers

    Google

  4. #4

    Post

    Thanks folks. I followed up some google search results.

    The following document gave a definite answer to one of my questions: http://www.usb.org/developers/data/usb_20g.pdf

    This doc says:
    "Today's USB connectors and full-speed cables will support the higher speeds of USB2.0 without any changes"

    This statement means, for example, that if I have a USB1.1 cable offering USB1.1 speeds between a USB1.1 PC and a USB1.1 peripheral, the same cable would be able to give me USB2.0 speeds when used with a USB2.0 PC and a USB2.0 peripheral.

    However, as you may recall, my immediate problem has got to do with a "USB-based cable", rather than a "regular" USB cable that connects a PC to a peripheral. The USB file transfer kits that I'm talking about use what I cautiously refer to as "USB-based cables", which I suspect might incorporate some proprietary h/w technology of their own between the 2 ends of the cable. So, I guess, to be truly sure about these file transfer kits, I should be putting the question to the guys who make them: "Will your kit work with USB2.0 PCs, and at what speeds?"

    many thanks,
    chaith

  5. #5
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    If I remember correctly when looking at such a device a little while back, it did include some kind of hardware between the ends of the cables......

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