From February, 2004 commentary:

The claims primarily revolve around a patent titled "High Performance Microprocessor Having Variable Speed System Clock," no. 5,809,336 in the U.S. Patent and Trademark Office.

In microprocessors, time is kept by a vibrating crystal. In the early days of the business, processors operated at the same pace of the vibrating crystal. Microprocessors, however, started to move much faster than the crystal, requiring an internal mechanism to keep the two synchronized, said Jim Turley, an independent chip analyst and a member of Patriot's scientific advisory board.

Around six months ago, Patriot's executives determined that they had a claim against PC makers using Pentium chips, Turley said. He did not comment on the merits of the suit but said "it looks like (the original inventors) were onto something clever."

The patent application was filed in June 1995, and itself grew out of a patent application from August 1989. The U.S. patent office granted the patent in September 1998.