A master computer was the central computer system controlling all aspects of technology for highly advanced computerized civilizations.
Bynaus[]
The sophisticated master computer on the planet Bynaus was with which virtually all Bynar were interconnected. It was an integral part of Bynar society, influencing their language and even their thought patterns. The coexistence also brought dependence, as a disruption in the computer's operation physically affected the Bynars.
In 2364, the computer and all equipment on the planet were rendered entirely inactive due to a large electromagnetic pulse from a supernova. Through an elaborate plan to keep the computer's files intact, the Bynars stole a Federation starship, the USS Enterprise-D, to temporarily house all of the files while the pulse passed. They also kidnapped William T. Riker and Jean-Luc Picard in the hope that they would restore the files to the computer once they became unconscious. (TNG: "11001001")
Shore Leave Planet[]
A main terminal of the control computer
Such a computer was used to control the machinery of the Shore Leave Planet.
During its aeons of operation, this master computer was tasked with scanning the memories of the visitors who came to the planet for recreation. The planet's machinery would create the objects that the visitors desired. The Keeper oversaw operation of the planet for many years, but when the USS Enterprise visited in 2269, they discovered the caretaker was dead. It hoped to take control of the Enterprise, who it thought was the master of its crew.
After discussions with Uhura, James T. Kirk, and Spock, it decided to remain on the Amusement Planet, continuing its original task as a way to have the galaxy come to it instead of conquering it. It granted the Enterprise crew shore leave on the condition that they continued the conversation, a duty with which Spock was tasked. (TAS: "Once Upon a Planet")
This computer was voiced by James Doohan.