computer science

Sketchpad

Sketchpad is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sketchpad rather than just read about it. In short: Sketchpad (a.k.a. Robot Draftsman) is a computer program written by Ivan Sutherland in 1963 in the course of his PhD thesis, for which he received the Turing Award in 1988, and the Kyoto Prize in 2012.

Key takeaways

Sketchpad belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sketchpad to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sketchpad from memory before moving on to harder problems.

Reference excerpt

Sketchpad (a.k.a. Robot Draftsman) is a computer program written by Ivan Sutherland in 1963 in the course of his PhD thesis, for which he received the Turing Award in 1988, and the Kyoto Prize in 2012. It pioneered human–computer interaction (HCI), and is considered the ancestor of modern computer-aided design (CAD) programs and as a major breakthrough in the development of computer graphics in general. For example, Sketchpad inspired the graphical user interface (GUI) and object-oriented programming. Using the program, Sutherland showed that computer graphics could be used for both artistic and technical purposes and for demonstrating a novel method of human–computer interaction.

History See History of the graphical user interface for a more detailed discussion of GUI development.

Software

Sketchpad was the earliest program ever to use a complete graphical user interface. The clever way the program organizes its geometric data pioneered the use of master (objects) and occurrences (instances) in computing and pointed forward to object-oriented programming. The main idea was to have master drawings which can be instantiated into many duplicates. When a master drawing is changed, then all instances change also. This was the first known form of the Entity-Component-System model: for example instead of encapsulating points inside of a line object, the points are stored in a ring buffer as described in pages 48 to 52 of the paper, and the line only points to them. This allowed moving one point to alter all the shapes that use it in a single operation. The structures in Sketchpad were also able to store pointers to functions, to achieve a different behavior depending on the kind of object. In figure 3.8 of the paper, the "instances generic block" stores several "subroutine entries" which are pointers to functions: "display", "howbig" etc. This was an early form of virtual functions. Geometric constraints was another major invention in Sketchpad, letting a user easily constrain geometric properties in the drawing: for instance, the length of a line or the angle between two lines could be fixed. As a trade magazine said, clearly Sutherland "broke new ground in 3D computer modeling and visual simulation, the basis for computer graphics and CAD/CAM". Very few programs can be called precedents for his achievements. Patrick J. Hanratty is sometimes called the "father of CAD/CAM" and wrote PRONTO, a numerical control language at General Electric in 1957, and wrote CAD software while working for General Motors beginning in 1961. Sutherland wrote in his thesis that Bolt, Beranek and Newman had a "similar program" and T-Square was developed by Peter Samson and one or more fellow MIT students in 1962, both for the PDP-1. The Computer History Museum holds program listings for Sketchpad.

Hardware Sketchpad ran on the MIT Lincoln Laboratory TX-2 (1958) computer at the Massachusetts Institute of Technology (MIT), which had 64k of 36-bit words. The user drew on the computer monitor screen with the recently invented light pen, which relayed information on its position by computing at what time the light from the scanning cathode-ray tube screen is detected. To configure the initial position of the light pen, the word INK was displayed on the screen, which, upon tapping, initialised the program with a white cross to continue keeping track of the pen's movement relative to its prior position. Of the 36 bits available to store each display spot in the display file, 20 gave the coordinates of that spot for the display system and the remaining 16 gave the address of the n-component element responsible for adding that spot to display. The TX-2 was an experimental machine and the hardware changed often (on Wednesdays, according to Sutherland). By 1975, the light pen and the cathode-ray tube with which it had been used had been removed.

Publications The Sketchpad program was part and parcel of Sutherland's Ph.D. thesis at MIT and peripherally related to the Computer-Aided Design project at that time. Sketchpad: A Man-Machine Graphical Communication System.

See also Comparison of CAD software

References

Bibliography Coons, Steven (1964). Fitch, John (ed.). "Computer Sketchpad" (episode). Science Reporter. Explains basic Sketchpad principles. Kay, Alan (16 July 2007). Sketchpad, by Dr. Ivan Sutherland with comments by Alan Kay (video). Palo Alto, California: Xerox PARC. Archived (Flash) from the original on 18 December 2009. Retrieved 25 April 2025 – via David Carroll; YouTube. Archive 2: Ghostarchive Kay, Alan (1987). "Pt 1". Doing with Images Makes Symbols (video presentation). University Video Communications – via Archive. Kay, Alan (21 February 2024). Written at London, England. Alan Kay's talk at UCLA 2024 February 21st (video). Los Angeles, California: Yoshiki Ohshima (大島芳樹). Kay narrates Sketchpad operation at 44:15–51:46. Retrieved 24 April 2025 – via YouTube. Müller-Prove, Matthias. "Graphical User Interface of Sketchpad". Germany: MProve. Sutherland, Ivan Edward (1980). Sketchpad: A Man-Machine Graphical Communication System (PhD thesis). New York: Garland Publishers. ISBN 0-8240-4411-8. Sutherland, Ivan Edward. Sketchpad: A man-machine graphical communication system (PDF) (PhD thesis). UK: CAM. Technical Report No. 574. Sutherland, Ivan Edward. "Sketchpad: A Man-Machine Graphical Communication System". AFIPS conference proceedings (PhD thesis). PL: ACI. Archived from the original on 2005-04-22. Yares, Evan (February 2013). "50 Years of CAD". Design World: 66–71.

External links Fitch, John; Coons, Steven; Johnson, Timothy (1964). Computer Sketchpad [Ivan Sutherland – Sketchpad Demo (1/2)] (video). Lexington, Massachusetts: MIT Lincoln Laboratory. Retrieved 6 January 2025 – via Association for Computing Machinery. Fitch, John; Johnson, Timothy; Roberts, Lawrence (1964). Computer Sketchpad [Ivan Sutherland – Sketchpad Demo (2/2)] (video). Lexington, Massachusetts: MIT Lincoln Laboratory. Retrieved 6 January 2025 – via Association for Computing Machinery. Sutherland, Ivan Edward (30 January 1963). Sketchpad: A Man-Machine Graphical Communication System (PDF) (Report). Lincoln Laboratory, Massachusetts Institute of Technology. Technical Report No. 296. Archived from the original on April 8, 2013. Retrieved 2007-11-03 – via Defense Technical Information Center.

Illustrations

Worked examples

Example 1 — a first encounter with Sketchpad

Start with the simplest possible case. Write down what Sketchpad claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sketchpad before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sketchpad ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sketchpad

In research: Sketchpad appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sketchpad in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sketchpad is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1963 software, Computer graphics, Graphical user interfaces, so understanding it makes those chapters shorter.
In everyday life: Look for Sketchpad outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sketchpad in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sketchpad means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sketchpad out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sketchpad in simple terms?

Why does Sketchpad matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sketchpad?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sketchpad.