Sketchpad was a revolutionary computer program written by Ivan Sutherland in 1963 in the course of his PhD thesis. It helped change the way people interact with computers. Sketchpad is considered to be the ancestor of modern computer-aided drafting (CAD) programs as well as a major breakthrough in the development of computer graphics in general. Ivan Sutherland demonstrated with it that computer graphics could be utilized for both artistic and technical purposes in addition to showing a novel method of human-computer interaction.

Sketchpad was the first program ever to utilize a complete graphical user interface. Sketchpad used an x-y point plotter display as well as the recently invented light pen. The clever way the program organized its geometric data pioneered the use of "objects" and "instances" in computing and pointed forward to object oriented programming. The main idea was to have master drawings which you could instantiate into many duplicates. If you changed the master drawing all the instances would change as well. Another major invention in Sketchpad was to let the user easily constrain selected geometrical properties in the drawing. For instance the length of a line or that two lines should have a specific angle between them. Sketchpad ran on the Lincoln TX-2 computer at MIT.

In 1963 most computers ran jobs in batch job mode only, using punch cards or magnetic tape reels submitted by professional programmers or engineering students. A considerable amount of work was required to make the TX-2 operate in interactive mode with a large CRT screen. When Sutherland had finished with it, it had to be reconverted to run in batch mode again. This involved some major hardware reconstruction as well as software work.

The Sketchpad program was part and parcel of Sutherland's Ph.D. thesis at MIT. It was reprinted in 1980 under the title Sketchpad: A Man-Machine Graphical Communication System. It is now out of print but several university libraries have copies and it is also present on the rare book market. For a PhD thesis it is remarkably clear and readable. A new electronic edition (3.9MB PDF) was published in 2003.

References

• Kay, Alan Doing with Images Makes Symbols Pt 1 Video presentation by Alan Kay that demonstrates Sketchpad (Sketchpad demo starts at 2:54).
• Sutherland, Ivan Edward. Sketchpad: A Man-Machine Graphical Communication System. New York: Garland Publishers, 1980. ISBN 0824044118.
• Sutherland, Ivan Edward. Sketchpad: A Man-Machine Graphical Communication System, a paper from AFIPS conference proceedings.