The earliest known publication of the term mouse as referring to a computer pointing device is in Bill English's July 1965 publication, "Computer-Aided Display Control".

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The plural for the small rodent is always "mice" in modern usage. The plural of a computer mouse is "mouses" and "mice" according to most dictionaries, but "mice" being more common. The first recorded plural usage is "mice"; the online Oxford Dictionaries cites a 1984 use, and earlier uses include J. C. R. Licklider's "The Computer as a Communication Device" of 1968.

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The trackball, a related pointing device, was invented in 1946 by Ralph Benjamin as part of a post-World War II-era fire-control radar plotting system called Comprehensive Display System (CDS). Benjamin was then working for the British Royal Navy Scientific Service. Benjamin's project used analog computers to calculate the future position of target aircraft based on several initial input points provided by a user with a joystick. Benjamin felt that a more elegant input device was needed and invented what they called a "roller ball" for this purpose.

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The device was patented in 1947, but only a prototype using a metal ball rolling on two rubber-coated wheels was ever built, and the device was kept as a military secret.

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Another early trackball was built by British electrical engineer Kenyon Taylor in collaboration with Tom Cranston and Fred Longstaff. Taylor was part of the original Ferranti Canada, working on the Royal Canadian Navy's DATAR (Digital Automated Tracking and Resolving) system in 1952.

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DATAR was similar in concept to Benjamin's display. The trackball used four disks to pick up motion, two each for the X and Y directions. Several rollers provided mechanical support. When the ball was rolled, the pickup discs spun and contacts on their outer rim made periodic contact with wires, producing pulses of output with each movement of the ball. By counting the pulses, the physical movement of the ball could be determined. A digital computer calculated the tracks and sent the resulting data to other ships in a task force using pulse-code modulation radio signals. This trackball used a standard Canadian five-pin bowling ball. It was not patented, since it was a secret military project.

 

Douglas Engelbart of the Stanford Research Institute (now SRI International) has been credited in published books by Thierry Bardini, Paul Ceruzzi, Howard Rheingold, and several others as the inventor of the mouse. Engelbart was also recognized as such in various obituary titles after his death in July 2013.

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By 1963, Engelbart had already established a research lab at SRI, the Augmentation Research Center (ARC), to pursue his objective of developing both hardware and software computer technology to "augment" human intelligence. That November, while attending a conference on computer graphics in Reno, Nevada, Engelbart began to ponder how to adapt the underlying principles of the planimeter to X-Y coordinate input. On November 14, 1963, he first recorded his thoughts in his personal notebook about something he initially called a "bug," which in a "3-point" form could have a "drop point and 2 orthogonal wheels." He wrote that the "bug" would be "easier" and "more natural" to use, and unlike a stylus, it would stay still when let go, which meant it would be "much better for coordination with the keyboard."

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In 1964, Bill English joined ARC, where he helped Engelbart build the first mouse prototype. They christened the device the mouse as early models had a cord attached to the rear part of the device which looked like a tail, and in turn resembled the common mouse. As noted above, this "mouse" was first mentioned in print in a July 1965 report, on which English was the lead author. On December 9, 1968, Engelbart publicly demonstrated the mouse at what would come to be known as The Mother of All Demos. Engelbart never received any royalties for it, as his employer SRI held the patent, which expired before the mouse became widely used in personal computers. In any event, the invention of the mouse was just a small part of Engelbart's much larger project of augmenting human intellect.