U

Ultimatte -

The trade name of a very high-quality, special-effects system used for background replacement and image composites.
U-matic -
A video cassette system using 0.75-inch tape format.
underrun -
Loss of data caused by the inability of a transmitting device or channel to provide data to the communication control logic (SDLC or BSC/SS) at a rate fast enough for the attached data link or loop.
unfreeze -
(1) To return to action after a freeze. (2) Enables updates to the video buffer. (3) Synonym for thaw.
unidirectional microphone -
A microphone that responds to sound from only one direction and is not subject to change of direction. (A unidirectional microphone is the type of microphone employed in computers capable of voice recognition.)
unload -
To eject the medium from the device.
user-defined message -
A private message sent directly to an I/O procedure by using the mmioSendMessage function. All messages begin with an MMIOM prefix, with user-defined messages starting at MMIOM_USER or above.
user interface -
The area at which a user and an object come together to interact. As applied to computers, the ensemble of hardware and software that allows a user to interact with a computer.
user's conceptual model -
A user's mental model about how things should work. Much of the concepts and expectations that make up the model are derived from the user's experience with real-world objects of similar type, and experience with other computer systems.

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