Microsoft Corp. is partnering with rival Novell, Inc. to improve interoperability of their software in a deal announced by the chief executives of both companies on Thursday.

Microsoft CEO Steve Ballmer and Novell CEO Ron Hovsepian announced details of a plan to link Windows and Novell's competing SUSE Linux software at a news conference in San Francisco.

"We're here to announce a set of agreements that will bridge the divide between open source and proprietary source software," Ballmer said.

"Microsoft and Novell are coming together to collaborate."

With proprietary source, or closed-source software, the underlying computer code is restricted and guarded by patent and other intellectual property protections. Microsoft's Windows is an example of proprietary source code.

In contrast, the open source software movement encourages access to the basic code that defines programs built with it. Individuals are then free to add to or modify the software without fear of legal repercussions. Linux is an example of this. SUSE Linux is Novell's version of Linux.

The agreements will help users of both companies' software run them side-by-side on the same computer or server, and improve the compatibility of different document formats.

Patent protection

The competitors also announced an agreement to provide each other's customers with patent coverage for their products. Neither company will make patent claims against their rivals' customers. The agreements will be in place until at least 2012.

"We won't assert our patents against individual, non-commercial open source developers" who write code for SUSE Linux, Ballmer pledged.

Hovsepian hailed the deal package as a breakthrough.

"This announcement gives our customers interoperability and peace of mind all in one," Hovsepian said.

Financial details of the agreements were not disclosed.

The companies will continue to compete in other areas, both executives stressed.

The deals will have no impact on Novell's antitrust lawsuit against Microsoft.

Asked whether the outstanding conflicts addressed by the agreements affected the lawsuit, Ballmer said, "We were able to clear up almost everything except that one."

The lawsuit, filed in 2004, alleges Microsoft used anticompetitive practices that were harmful to Novell's earlier WordPerfect office software suite business.