rom the late 1980's through the mid- 90's, one software company after another, from start-ups like the Go Corporation to giants like Microsoft, pursued the same vision: a computer that would take its orders from a pen. And one after another they failed, sometimes infamously.
Now Microsoft is betting that the time and the technology have arrived.
At his keynote speech at the giant Comdex computer show next week in Las Vegas, Microsoft's chairman, William H. Gates, will demonstrate a prototype of a portable computing slate the size of an 8 1/2- by-11-inch notebook, operated not with a keyboard but with a stylus.
In recent weeks the company has begun testing the first of several hundred prototypes. Microsoft does not plan to make such computers commercially, but if all goes well, it hopes that hardware makers will begin selling them by 2002.
Unlike today's hand-held computers, used largely as organizers, the tablet computer being developed by Microsoft will run the same Windows-based programs run by a desktop computer.
Because of the increasing availability of wireless office networks, it will permit the computer user to stay connected to the Internet even while sitting in meetings.
"Handwriting recognition has always been a cool computer science problem," said Alex Loeb, the general manager of the Microsoft Tablet PC group, referring to the challenge of getting machines to recognize the words of writers who frequently cannot decipher even their own scrawl.
And whatever the optimism of Mr. Gates and his team, many industry veterans remain skeptical that Microsoft will be able to fashion a pen-based version of the Windows operating system that will create a market as broad as today's PC industry.
That perspective comes from bitter experience for companies like Go, Eo, Grid, Momenta, Apple Computer, AT&T and Microsoft. Indeed, the pen computing market became a bitterly contested arena in which many in the industry believed that Microsoft's effort, PenWindows, existed only to forestall competitors.
At the time there were a variety of approaches, ranging from systems that tried to recognize cursive handwriting or individual characters to those that merely captured "digital ink," leaving the problem of recognition to the writer.
Of all those efforts, one notably succeeded: that of Palm Computing, whose operating system made possible the original Palm Pilot. It drastically simplified and limited the tasks the hand-held device performed, it fit in a shirt pocket, and it forced the computer user to conform to a highly structured character recognition system called Graffiti. Microsoft developed its own operating system, Windows CE, for competing devices.
But creating a script-based system with enough sophistication and maneuverability for a full-fledged PC is a challenge of a different order.
Last week, Bert Keely, an engineer in Microsoft's tablet PC effort, gave a brief demonstration of a note-taking application that will be at the heart of the new system.
Instead of converting the user's writing to text on the screen, displaying one character before the next can be written, the system would simply capture digital ink strokes, while recognition would take place in the background. Later, the user could convert the script to text and check it for mistakes, with the computer offering possible alternatives for each word. The system would also index the words to allow the user to search the text easily.