The upper hand, legal experts say, was certainly held by Ms. Kroes. “She was really negotiating from a position of strength, which she did not have before the ruling by the Court of First Instance,” said Andrew I. Gavil, a law professor at Howard University.

The move by Microsoft, according to industry analysts, is a significant step that the company wants to remove the lingering cloud that the European antitrust has cast over the company’s business and its stock price.

“Financially, the antitrust issues have not had a material effect on Microsoft, and it’s not yet clear that this agreement will have much impact on the software market,” said Charles di Bona, an analyst with Sanford C. Bernstein. “But it does help to remove the European cudgel that has been hanging over the company’s head. It removes an element of uncertainty, which shareholders hate.”

Microsoft has paid nearly 1 billion euros, or $1.43 billion, in fines since the commission’s initial ruling and could face up to 1.6 billion euros more, which began accumulating in December 2005 after Microsoft failed to provide the protocols. Ms. Kroes said she would decide before the end of the year whether Microsoft must pay the additional fines.

Ms. Kroes cast the agreement as a big win for Microsoft’s rivals, especially companies that rely on open-source software like the Linux operating system, an increasingly popular alternative to Microsoft. Linux has done particularly well on server computers, where its main competitor is Microsoft’s server software.

To thrive in the marketplace, open-source software must work well with Microsoft’s desktop programs, notably the Windows personal computer operating system. More than 90 percent of all PC’s run on Windows.

The European order mandates that Microsoft share its technology information on fair terms, so that competing software can work smoothly, or interoperate, with Windows desktop software. It was those terms of interoperability that will be much more favorable to Microsoft competitors, so that the company’s dominance in product cannot thwart competition in another, closely related software market.