The system was called NLS, or oN-Line System, because it was also networked between multiple computers.

The display system was based on vector graphics technology and could display both text and solid lines on the same screen. Because of limited memory space in the mainframe computer, it could only display upper-case characters, although true upper-case was displayed by the use of a short horizontal line directly above any capitalized letters.

The oN-Line System display, keyboard and mouse

Douglas' hands operated three input devices: a standard typewriter-style keyboard, a five-key "chording keyboard" (combinations of the five keys could produce 2^5 or 32 separate inputs, enough for all the letters of the alphabet), and a small rectangular box about the size of a couple of juice boxes with three buttons near the top, connected to the computer with a long wire.

This was the mouse, invented by Douglas himself and built by one of his engineers. Nobody knew who first started calling it a mouse, but the name stuck back then, and has remained ever since. Mechanically it was slightly different from modern mice in that the two circular wheels connected to the internal potentiometers rolled directly on the table surface, instead of being manipulated by a single mouse ball rubbing against rollers. However, to the end user it operated virtually identically to a modern mouse. Other input devices had been tried (such as touch screens and light pens), but user testing found the mouse to be the most natural way to manipulate an on-screen cursor. This remains true today.

Close-up of the keyboard and mouse

With the invention of the mouse came the invention of the mouse pointer, which in this system was a stick arrow, about the height of a single character, pointing straight up. This was called a "bug" by Douglas' team, but this term did not survive into modern use. When objects were selected, the "bug" would leave dots on the screen to mark this action.

Many of the things demonstrated in this marathon session seemed to come from decades in the future, and most of the people watching it were hard pressed to even understand all of what they were seeing. The demo featured hypertext linking, full-screen document editing, context-sensitive help, networked document collaboration, e-mail, instant messenging, even video conferencing! It was all somewhat overwhelming, and due to limitations in the video system, sometimes difficult to tell what was going on. For example, NLS supported multiple windows, but there was no obvious way to indicate boundaries between them (such as window borders, title bars, etc)