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Flash drive can't recognized by windows

By gully
Apr 11, 2007
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  1. Is there are possibility that flash drive or external hdd can't recognized by windows because of different volt between back and front usb ports? Or could it be the usb cable have different volt? If yes.. how this could happened? I’ve read Flash drive recovery procedures (by Tedster) and view other threads but I can't get my answer.
  2. Nodsu

    Nodsu TS Rookie Posts: 9,431

    Yes, an external hard drive may not get enough power from an USB port. That's why they come with two USB connector or an AC adapter.

    Flash devices and externally powered hard drives do not have this problem.
  3. rf6647

    rf6647 TS Maniac Posts: 931

    I will address a different failure mode. The usb controller for the selected port may have stopped operating. Disconnect usb devices from this controller. Restart the computer. Reconnect usb devices. Observe the reports as each usb device registers with the device manager.

    I do not have the experience to assert this is either marginal hardware or a Windows glitch. My current experience involves a multifunctional printer that goes offline. The usb controller disappears from the device manager list. The method above solves my problem.

    Somewhere in the TS forums is a discussion on this topic (or nearly so) where the advice given was to power off the computer, wait 30 minutes, power on the computer. I could not find it again.
  4. CraigMc

    CraigMc TS Rookie Posts: 50

    It is also good practise, depending on the size of your flash drive, to use the USB ports on the back of your computer rather than the front ones. The reason for the different voltage between front and back is that the back ones are the "actual" USB ports, built into your motherboard and powered from the motherboard, the front ones are from a header block and are essentially like a non-powered USB hub.
  5. Nodsu

    Nodsu TS Rookie Posts: 9,431

    There is no such thing as a different voltage causing problems. The USB standard states the exact voltage range that has to be supplied on the USB power wires. And all USB devices that draw power from USB have to work within that voltage range. That's what we have standards for.

    Now, amperage is a completely different matter. The maximum current supported by different USB ports may be different and some high-power devices may indeed fail on some ports.
  6. CraigMc

    CraigMc TS Rookie Posts: 50

    Amperage - that would be the word I was looking for :)
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