USB Device speed
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The USB standard (2.0) allows different speeds to be used
for each device. This way, slow input devices, such as a
keyboard or a mouse, can transfer data at low rate, leaving
more of the available bandwidth to other devices.
Other devices, such as printers, will generally use a higher
speed to transfer towards them.
The USB 2.0 standard recognises three different speeds:
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The symbol in the left most column will be displayed in the Interface box
to illustrate the speed of that device. Please note that all interfaces in
a device always have the same speed.
The naming conventions for the speeds may appear somewhat
strange, especially, since FULL speed is slower than Hi speed. The reason
for this is that both LOW and FULL speed were already defined in the USB 1.0
standard, when the higher speed was introduced in USB 2.0.
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Speeds on USB 1.1
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A USB 1.1 card is only capable of using the lowest two speeds,
i.e. LOW (1.5 Mb/s) and FULL (12 Mb/s). The highest speed
(480 Mb/s) can only be used on USB 2 cards and require additional
support from your operating system. However, all USB 2.0 devices
are downwards compatible with the USB 1.1 standard. In other words:
all Hi-speed devices, such as external harddiscs, also support
FULL speed (12 Mb/s), enabling you to use the device, albeit at
a lower speed.
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USB logos
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Any new USB devices available today, are likely to show one of these
USB logos on their packaging. First of all a manuafacturer is only
allowed to show this logo, if the device has passed compliance testing
with the USB Implementers Forum (USB-IF). Secondly
the logo may indicate that the device supports the highest USB speed
available (i.e. Hi-speed, 480 Mb/s).
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This logo indicates that a product has succesfully completed the USB-IF
Compliance Testing Program and supports the Hi-Speed USB data transfer
rate of 480 Mb/s. Products that can take advantage of the faster data
transfer rates of Hi-Speed USB include products such as CD-RWs, DVD drives,
flash card readers, digital cameras and scanners.
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For products that do not require the higher transfer speeds of Hi-Speed USB, look for
the Certified USB logo. This logo indicates that the product has succesfully completed
the USB-IF Compliance Testing Program for products operating at
original USB speeds (1.5 MB/s and 12 Mb/s).
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© Copyright Paul Reuvers
X-Ample Technology bv
usb@xat.nl
Last changed: Last changed: Friday, 25 July 2003 - 12:19 CET.
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