The most common way to connect external
devices to a computer is USB. USB provides expandability without the
complexity of connecting internal devices such as PCI cards. Connecting
USB devices is so simple that most end users can connect and configure
USB devices without help from the support center (provided that they
have sufficient privileges). However, users do occasionally experience
problems with USB devices. The following sections provide guidance for
troubleshooting USB problems.
How to Solve USB Driver and Hardware Problems
If you do experience problems, following these steps might solve them:
1. | Restart
the computer. Some software might require the computer to be restarted
before functioning properly. Additionally, restarting the computer
forces Windows Vista to detect the USB hardware again.
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2. | Install updated driver software, if available. Check Windows Update and the hardware manufacturer’s website for updates.
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3. | Uninstall
the device’s driver and software, disconnect the USB device, restart
the computer, and then follow the manufacturer’s instructions to
reinstall the software. Many USB devices require a driver. Typically,
the driver should be installed before connecting the USB device. If you
are experiencing problems with a USB device, the most likely cause is a
driver problem.External storage devices such as USB flash
drives and external hard drives typically do not require a driver
because the required software is built into Windows.
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4. | Disconnect
the USB device and reconnect it to a different USB port. This can cause
Windows to detect the device as new and reinstall required drivers.
Additionally, this will solve problems related to a specific USB port,
such as a failed port or power limitations.
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5. | Replace the USB cable with a new cable, or a different cable that you know works properly.
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Understanding USB Limitations
If
you installed the USB device’s software correctly and you are using the
most up-to-date version of the driver, you still might have problems
because of USB’s physical limitations. Limitations that can cause
problems include:
Insufficient power
Many USB devices receive power from the USB port. Connecting too many
unpowered devices to a USB hub can result in a power shortage, which
can cause a USB device to not respond properly. This is particularly
common when using an unpowered external USB hub. To quickly determine
whether a problem is power-related, disconnect other USB devices, and
connect each USB device directly to the computer one by one. If devices
work when connected separately but fail when connected simultaneously,
the problem is probably power-related. Decrease the number of devices,
or add a powered USB hub.
Excessive length
USB devices can be no more than 5 meters away from the USB hub it is
connected to. While USB devices will never ship with cables longer than
5 meters, some users connect USB extenders to allow longer distances.
Depending on the quality of the cable and possible sources of
interference, you might experience problems with shorter distances. To
determine whether length is the source of problems, remove any USB
extenders and connect the USB device directly to the computer.
Too many devices
USB can support up to a maximum of 127 devices connected to a single
USB host controller, which is more than enough for the vast majority of
client computer scenarios. You can have a maximum of seven layers of
USB hubs connected to the computer’s USB host controller, and no more
than five external hubs.
Insufficient bandwidth
Most USB devices are designed to work within USB bandwidth limitations.
However, video cameras in particular, might need more bandwidth than
USB is capable of providing. If you receive a “Bandwidth Exceeded”
message, first try disconnecting other USB devices. If the message
continues to appear, attempt to reduce the bandwidth used by the device
by lowering the resolution of the camera. For best results with a video
camera, connect it to a IEEE 1394 (also known as Firewire or iLink)
port.
Note
If
you see the message, “Hi-speed USB device is plugged into non-hi-speed
USB hub,” the USB device is USB 2.0, but the USB port is an earlier
version. The device will probably work, but it will work slowly. You
can improve performance by adding a USB 2.0 port to the computer. |
