Two IBM-compatible computers were unveiled.

The powerful mainframe computers were introduced by National Advanced Systems, the California company that sells large-scale computers in the United States for Hitachi Ltd. of Japan. NAS sells Hitachi-made computers that can run software and related equipment designed for IBM computers. The new NAS mainframes are in response to IBM’s Feb. 12 unveiling of the first two models of its new generation of top-of-the-line computers, the 3090 series, also known as Sierra. National’s two machines are the AS-XL models 60 and 80, which are comparable in performance to the two IBM machines, the company said.