Platform Solutions (PSI), a company that makes a system that allows IBM mainframe operating systems to run on Itanium-based hardware, is facing a lawsuit from Big Blue.

IBM filed a federal lawsuit against PSI alleging patent infringements and breach of contract, according to the lawsuit filed late last month in U.S. District Court for the Southern District of New York.

The lawsuit cites letters between the two companies disagreeing over licensing issues. The correspondence extends back several years, but IBM said the dispute came to a head when PSI began lining up customers.

Beta users include Lufthansa Systems, and general product availability is planned for early next year, according to PSI.

PSI technology allows z/OS and OS/390 operating systems and applications to run on Itanium systems. In its lawsuit, IBM said it is refusing to license its operating systems for that use.

"IBM has a strong interest in ensuring that z/OS is not used on computer systems with which z/OS is not fully compatible or used in ways that have the potential to undermine either the reputation of z/OS for accuracy, data integrity, and reliability or customers acceptance of z/OS for mission-critical applications," the company said in the lawsuit. IBM refers to PSI's product as an emulator, a characterization disputed by the company, which calls its system an open mainframe computer.

Christian Reilly, PSI's marketing director, said what his company brings is competition on the mainframe platform. "This market is pretty much a sole source for hardware in the z/OS market -- it's a US$4 billion market, and customers have expressed a strong demand for choice," he said.

IBM said in its lawsuit that at one point, PSI threatened an antitrust lawsuit. Reilly said that he couldn't comment on the specifics of the lawsuit and that the company has not filed its response yet.

John Phelps, an analyst at Gartner, said PSI is trying to provide an alternative hardware platform to the mainframe, but "software costs have been the biggest problem in the mainframe space, and I didn't know how they were going to solve software costs."

PSI's executive team includes former Amdahl and IBM executives. Amdahl, which was acquired by Fujitsu in 1997, made IBM mainframe-compatible hardware but didn't produce a 64-bit system for the z/OS.