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 $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 Inc., 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 Corp. 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.