This unflown device was probably used to test software for the Space Shuttle Multiplexer/Demultiplexer, which processed communications signals. On the top of this device is a set of "EEPROMS" -- electrically-erasable programmable read-only memory chips. As the software is developed, the contents of these chips could be modified by shining u-v light on them. Once the software is validated, it is stored on Read-only chips that would be installed inside the housing.
NASA transferred this to the Smithsonian in 2016.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.