Pen computing refers to a computer user-interface using a pen (or stylus) and tablet, rather than devices such as a keyboard, joysticks or a mouse.
Pen computing is also used to refer to the usage of mobile devices such as wireless tablet personal computers, PDAs and GPS receivers. The term has been used to refer to the usage of any product allowing for mobile communication. An indication of such a device is a stylus, generally used to press upon a graphics tablet or touchscreen, as opposed to using a more traditional interface such as a keyboard, keypad, mouse or touchpad.
Historically, pen computing (defined as a computer system employing a user-interface using a pointing device plus handwriting recognition as the primary means for interactive user input) predates the use of a mouse and graphical display by at least two decades, starting with the Stylator  and RAND Tablet systems of the 1950s and early 1960s.
General techniques of pen computing 
User interfaces for pen computing can be implemented in several ways. Actual systems generally employ a combination of these techniques.
Pointing/locator input 
The tablet and stylus are used as pointing devices, such as to replace a mouse. While a mouse is a relative pointing device (one uses the mouse to "push the cursor around" on a screen), a tablet is an absolute pointing device (where one puts the stylus describes exactly where the cursor goes).
There are a number of human factors to be considered when actually substituting a stylus and tablet for a mouse. For example, it is much harder to target or tap the same exact position twice with a stylus, so "double-tap" operations with a stylus are harder to perform if the system is expecting "double-click" input from a mouse.
A finger can be used as the stylus on a touch-sensitive tablet surface, such as with a touchscreen.
Handwriting recognition 
The tablet and stylus can be used to replace a keyboard, or both a mouse and a keyboard, by using the tablet and stylus in two modes:
- Pointing mode: The stylus is used as a pointing device as above.
- On-line Handwriting recognition mode: The strokes made with the stylus are analyzed as a "electronic ink", by software which recognizes the shapes of the strokes or marks as handwritten characters. The characters are then input as text, as if from a keyboard.
Different systems switch between the modes (pointing vs. handwriting recognition) by different means, e.g.
- by writing in separate areas of the tablet for pointing mode and for handwriting-recognition mode.
- by pressing a special button on the side of the stylus to change modes.
- by context, such as treating any marks not recognized as text as pointing input.
- by recognizing a special gesture mark.
The term "on-line handwriting recognition" is used to distinguish recognition of handwriting using a real-time digitizing tablet for input, as contrasted to "off-line handwriting recognition", which is optical character recognition of static handwritten symbols from paper.
Direct manipulation 
The stylus is used to touch, press, and drag on simulated objects directly. The Wang Freestyle system  is one example. Freestyle worked entirely by direct manipulation, with the addition of electronic "ink" for adding handwritten notes.
Gesture recognition 
This is the technique of recognizing certain special shapes not as handwriting input, but as an indicator of a special command.
For example, a "pig-tail" shape (used often as a proofreader's mark) would indicate a "delete" operation. Depending on the implementation, what is deleted might be the object or text where the mark was made, or the stylus can be used as a pointing device to select what it is that should be deleted. With Apple's Newton OS, text could be deleted by scratching in a zig-zag pattern over the text which the user desired to remove.
Recent systems have used digitizers which can recognize more than one "stylus" (usually a finger) at a time, and make use of Multi-touch gestures.
The PenPoint OS was a special operating system which incorporated gesture recognition and handwriting input at all levels of the operating system. Prior systems which employed gesture recognition only did so within special applications, such as CAD/CAM applications  or text processing.
Pen computing has very deep historical roots. The depth of these roots can be quite surprising to people who are only familiar with current commercial products. For example, the first patent for an electronic tablet used for handwriting, the telautograph, was granted in 1888. What is probably the first patent for a system that recognized handwritten characters by analyzing the handwriting motion was granted in 1915. The first publicly demonstrated system using a tablet and handwriting text recognition instead of a keyboard for working with a modern digital computer dates to 1956.
In addition to many academic and research systems, there were several companies with commercial products in the 1980s: Pencept, Communications Intelligence Corporation, and Linus were among the best known of a crowded field. Later, GO Corp. brought out the PenPoint OS operating system for a tablet PC product: one of the patents from GO corporation was the subject of recent infringement lawsuit concerning the Tablet PC operating system.
The following timeline list gives some of the highlights of this history:
- Before 1950
- 1888: U.S. Patent granted to Elisha Gray on electrical stylus device for capturing handwriting.
- 1915: U.S. Patent on handwriting recognition user interface with a stylus.
- 1942: U.S. Patent on touchscreen for handwriting input.
- 1945: Vannevar Bush proposes the Memex, a data archiving device including handwriting input, in an essay As We May Think.
- Tom Dimond demonstrates the Styalator electronic tablet with pen for computer input and handwriting recognition.
- Early 1960s
- Late 1960s
- The first commercially available tablet-type portable computer was the GRiDPad from GRiD Systems, released in September. Its operating system was based on MS-DOS.
- Wang Laboratories introduces Freestyle. Freestyle was an application that would do a screen capture from an MS-DOS application, and let the user add voice and handwriting annotations. It was a sophisticated predecessor to later note-taking applications for systems like the Tablet PC. The operating system was MS-DOS
- The Momenta Pentop was released.
- GO Corp announced a dedicated operating system, called PenPoint OS, featuring control of the operating system desktop via handwritten gesture shapes. Gestures included "flick" gestures in different directions, check-marks, cross-outs, pig-tails, and circular shapes, among others.
- Portia Isaacsen of Future Computing estimates the total annual market for pen computers such as those running the PenPoint OS to be on the order of $500 Million.
- NCR released model 3125 pen computer running MS-DOS, Penpoint or Pen Windows.
- The Apple Newton entered development; although it ultimately became a PDA, its original concept (which called for a larger screen and greater sketching capabilities) resembled that of a tablet PC.
- Sam Tramiel of Atari Corp. presented the "ST-Pad" (codenamed "STylus") at the CeBIT '91 in Hanover, Germany. The computer never went into production.
- The IBM releases the ThinkPad, IBM's first commercialized portable tablet computer product available to the consumer market, as the IBM ThinkPad 750P and 360P
- Apple Computer announces the Newton PDA, also known as the Apple MessagePad, which includes handwriting recognition with a stylus.
- Amstrad release the "Pen Pad" or PDA6000, a similar pen-based device. It did not achieve commercial success.
- AT&T introduced the EO Personal Communicator combining PenPoint with wireless communications.
- BellSouth released the IBM Simon Personal Communicator, an analog cellphone using a touch-screen and display. It did not include handwriting recognition, but did permit users to write messages and send them as faxes on the analog cellphone network, and included PDA and Email features.
- Windows Vista released for general availability. Vista included the functionality of the special Tablet PC edition of Windows XP.
- In April 2008, as part of a larger federal court case, the gesture features of the Windows/Tablet PC operating system and hardware were found to infringe on a patent by GO Corp. concerning user interfaces for pen computer operating systems. Microsoft's acquisition of the technology is the subject of a separate lawsuit.
- HP releases the second MultiTouch capable tablet: the HP TouchSmart tx2z.
See also 
- Gesture recognition
- Handwriting movement analysis
- Handwriting recognition
- Interactive whiteboard
- Laser pointer (e.g. highlighting)
- Light pen
- Sketch recognition
- Dimond, T.L. (1957-12-01), Devices for reading handwritten characters, Proceedings of Eastern Joint Computer Conference, pp. 232–237
- Groner, G.F. (1966-08), Real-Time Recognition of Handprinted Text, Memorandum RM-5016-ARPA, RAND Corporation
- WANG Freestyle demo, Wang Laboratories, 1989, retrieved 2008-09-22
- Computerized Graphic Processing System: System User's Manual, Applicon Incorporated, 1973-09-01
- Newman, W.M. (1973-09-01), The Ledeen Character Recognizer, Principles of Interactive Computer Graphics, McGraw-Hill, pp. 575–582
- Coleman, Michael L. (1969), Text editing on a graphic display device using hand-drawn proofreader's symbols, from Pertinent Concepts in Computer Graphics: Proceedings of the 2nd University of Illinois Conference on Computer Graphics, University of Illinois Press
- Gray, Elisha (1888-07-31), Telautograph, United States Patent 386,815 (full image)
- Goldberg, H.E. (1915-12-28), Controller, United States Patent 1,117,184 (full image)
- Dimond, Tom (1957-12-01), Devices for reading handwritten characters, Proceedings of Eastern Joint Computer Conference, pp. 232–237, retrieved 2008-08-23
- Mintz, Jessica (2008-04-04), Microsoft to Appeal $367M Patent Ruling, The Associated Press, retrieved 2008-09-04
- Gray (1888-07-31), Telautograph, United States Patent 386,815
- Goldberg, H.E. (1915-12-28), Controller, United States Patent 1,117,184
- Moodey, H.C. (1942-12-27), Telautograph System, United States Patent 2,269,599
- Moodey, H.C. (1942-12-27), Telautograph System, United States Patent 2,269,599 (full image)
- Bush, Vannevar (1945-07-15), As We May Think, The Atlantic Monthly
- RAND Tablet, 1961-09-01
- 50 Years of Looking Forward, RAND Corporation, 1998-09-01
- Pencept Penpad (TM) 200 Product Literature, Pencept, Inc., 1982-08-15
- Inforite Hand Character Recognition Terminal, Cadre Systems Limited, England, 1982-08-15
- Users Manual for Penpad 320, Pencept, Inc., 1984-06-15
- Software Control at the Stroke of a Pen, Pencept, Inc., 1985, retrieved 2009-05-21
- Handwriter (R) GrafText (TM) System Model GT-5000, Communication Intelligence Corporation, 1985-01-15
- The BYTE Awards: GRiD System's GRiDPad, BYTE Magazine, Vol 15. No 1, 1990-01-12, p. 285
- Lempesis, Bill (1990-05), What's New in Laptops and Pen Computing, Flat Panel Display News
- Agulnick, Todd (1994-09-13), Control of a computer through a position-sensed stylus, United States Patent 5,347,295
- Agulnick, Todd (1994-09-13), Control of a computer through a position-sensed stylus, United States Patent 5,347,295 (full image)
- NCR announces pen-based computer press release (– Scholar search), archived from the original on 2008-05-02, retrieved 2007-04-20[dead link]
- Penpoint OS shipping press release (– Scholar search), archived from the original on 2007-08-30, retrieved 2007-04-20[dead link]
- Lenovo - The history of ThinkPad
- Trends at COMDEX Event 1999, retrieved 2008-08-11
- Microsoft (2005), Windows XP Tablet PC Edition 2005 Hardware Requirements, www.microsoft.com, retrieved 2009-03-14
- Fingerworks, Inc. (2003), iGesture Game Mode Guide, www.fingerworks.com, retrieved 2009-04-30
- MacEssentials (2007-08-02), Rubrik Apple: Das Lexikon der Fingersprache, www.mac-essentials.de, retrieved 2009-05-16
- HP TouchSmart tx2z, HP, retrieved 2008-11-28
- The Unknown History of Pen Computing contains a history of pen computing, including touch and gesture technology, from approximately 1917 to 1992.
- Annotated bibliography of references to handwriting recognition and pen computing
- A number of links to pen computing resources.
- Digital Ink, Breakthrough Technology in Tablet PC, Brings the Power of the Pen to the Desktop
- Notes on the History of Pen-based Computing (Youtube)