RUSSELS, Nov. 14 - Sun Microsystems and Real Networks, two companies that have the most to gain if European Union regulators force Microsoft to change the way that it operates, presented their arguments on the third and final day of a closed hearing in the antitrust proceedings Friday.
Neither company would comment on the details of its presentation, but Real Networks was expected to warn regulators that if Microsoft's business practices went unchecked, it would soon have a stranglehold over all sound and video content transmitted through computers and hand-held devices like portable phones.
Real Networks makes the Real One media-playing software that competes with Media Player from Microsoft.
The European Commission said in August that by embedding Media Player into Windows, Microsoft was abusing the dominant position of its operating system to corner the media-playing software market.
Microsoft argues that bundling Media Player into Windows achieves efficiencies that eventually benefit the consumer.
It does not want to change this practice, partly because its strategy for many new applications also relies on their belonging inside Windows, and it fears that by agreeing to unbundle Media Player it will be setting a dangerous precedent.
Sun is supporting the commission's efforts to force Microsoft to disclose enough Windows computer code to allow rivals to devise server software that works as well with Windows as Microsoft's own server software.
After the hearing the European Commission will produce a draft ruling, possibly as soon as next month.
The draft will outline the changes that the commission wants Microsoft to make to its business model and the size of the fine that it intends to impose on the company for having broken the antitrust rules of the European Union.
It will then present the draft to regulators from the 15 member nations of the union, who were also present at this week's hearing.
If the national regulators support the proposed ruling, the commission would then make it final.
The European competition commissioner, Mario Monti, would present it to his fellow commissioners, probably in the first two months of next year, and they would vote on whether or not to go ahead with the ruling.
Microsoft is expected to try to reach a settlement during this process. Microsoft said in a statement on Friday that it wanted to "narrow the differences" with its opponents.
