The three button Alto mouse enabled the first bitmapped and overlapping windows display, known as a graphical user interface (GUI). The Alto dates to March of 1973. It looks like a small slightly swelled and rounded rectangular beige plastic box with three large lozenze shaped buttons that appear to run together. "The buttons are named red, yellow, and blue, although the physical buttons are all black." [Byte 1981]
John Bordynuik, who furnished these detailed photos, completely refurbished an Alto I computer.
The Alto I mouse registers movement by its large steel ball at its cord end. The ball's relative position determines the placement of the cursor on the computer screen. Bill English managed the development of the mouse for the first Alto computer [Computer History Museum]. Jack Hawley worked on this mouse for SRI (Stanford Research Institute) and later recycled much of its mechanical design for his 1983 Mark II X063X mouse. The Alto I mouse's motherboard is embossed with "M-3" and "HAWLEY-XEROX MOUSE," along with the circuit board wire outlines marked with plus (+) and minus (-) poles.
Notice inside the mouse three black switch boxes with red switches which the mouse buttons activate. Drums and brushes for the X and the Y axes send signals to the computer when the large ball bearing moves. The tracking ball is housed in a metal case with bearings. Two smaller ball bearings at the wrist edge within the bottom plate of the mouse act as gliders. A thin black electrical cord attaches the mouse to the Alto with a DE-9 pins connector. Some photos show a different connector probably used to adapt to different machines.
A later version of the Alto mouse looks identical to the original 3-button mouse on top but it uses an optical design. The bottom of that mouse looks like the later "Star" optical mouse. The optical design must have won out due to the maintenance of the steel ball.
According to Geoff Thompson, who was at PARC during 1972 - 81, "You didn't really 'own' a mouse when you had possesion of an Alto, you just checked them out cause they weren't too reliable. They would pick up dirt, get gummed up and not track anymore. When that happened, you would just unplug it, take it into the lab and put it into the box that said 'Dead Mice' on it, grab a cleaned one from the 'Clean Mice' box and you were back in business."
One version of the Alto mouse had three horizontal buttons, one of red, yellow and blue. Like the Hawley mouse with colored buttons, the Alto mouse buttons were colored keyed to the instructions for applications like a "Red click" or "Yellow click." Apparently the vertical button arrangement won out. Too bad the colors went away.