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USB X-TENDER
Appendix D: Device Speeds
USB devices can communicate at either of two top
speeds. “Low-speed” devices communicate at up to
1.2 Mbps, while “full-speed” devices communicate at up
to 12 Mbps. Manufacturers of USB devices will typically
implement a device as “low-speed” or “full-speed”
depending on what they’re designed to do:
•
Low-speed
A mouse, for example, will always be implemented
as a “low-speed device” because it only needs to
communicate the coordinates of a single point or
the status of a few buttons. This can be done easily
at 1.2 Mbps. Most other pointing devices,
including keyboards, touchscreens, trackballs, and
joysticks, will also be implemented as low-speed
devices.
•
Full-speed
A video camera, on the other hand, will always be
implemented as a full-speed device, because it
must communicate the status of a large array of
video pixels points up to 30 times each second,
which can easily require 12 Mbps (and strain even
that limit). Other devices that have to send or
receive massive amounts of video, audio, or other
information in real time—including scanners,
