All software published in the United States is protected by strong copyright and trademark protection. Microsoft Excel, for example, cannot be copied, nor can its association with Microsoft be removed. But a patent goes well beyond this. It protects even the underlying concepts from being used by others -- for 20 years.

As recently as the 1970's, software developers relied solely upon copyrights and trademarks to protect their work. This turned out rather well for Microsoft. Had Dan Bricklin, the creator of VisiCalc, the spreadsheet that gave people a reason to buy a personal computer, obtained a patent covering the program in 1979, Microsoft would not have been able to bring out Excel until 1999. Nor would Word or PowerPoint have appeared if the companies that had brought out predecessors obtained patent protection for their programs.

Mr. Bricklin, who has started several software companies and defensively acquired a few software patents along the way, says he, too, would cheer the abolition of software patents, which he sees as the bane of small software companies. "The number of patents you can run into with a small product is immense," he said. As for Microsoft's aggressive accumulation in recent years, he asked, "Isn't Microsoft the poster child of success without software patents?"

So why didn't Mr. Bricklin file for a patent for VisiCalc in 1979? Patents for software alone were not an option then. He consulted a patent attorney who said that the application would have to present the software within a machine and that the odds were long that the ploy would succeed. The courts regarded software as merely a collection of mathematical algorithms, tiny revelations of nature's secrets -- not as an invention, and thus not patentable.

The legal environment changed not because of new legislation, but by accident. One important ruling here and another there, and without anyone fully realizing it, a new intellectual-property reality had evolved by the end of the 1980's. Now software could enjoy the extraordinary protection of a patent, protection so powerful that Thomas Jefferson believed that it should be granted in only a few select cases.

Making the best possible argument for Microsoft's newly acquired passion for patents is a job that falls to Brad Smith, the company's senior vice president and general counsel. Last week, we discussed the changing legal landscape in the 1990's. Microsoft had not taken an interest in patents in its early years because, as Mr. Smith said, "We thought we could rely on copyright." The courts changed the rules, and Microsoft had to respond like everyone else.

Why did Microsoft increase its patent-application target so sharply just last year?

"We realized we were underpatenting," Mr. Smith explained. The company had seen studies showing that other information technology companies filed about two patents for every $1 million spent on research and development. If Microsoft was spending $6 billion to $7.5 billion annually on its R&D, it would need to file at least 3,000 applications to keep up with the Joneses.