NEC Calls New Computer World’s Fastest : Mainframes: Analysts say the new system’s incompatibility with IBM products will hurt sales.

Japan’s NEC Corp. on Wednesday unveiled what it said is the world’s fastest mainframe computer.

NEC said the new ACOS System 3800 executes a maximum 500 million instructions per second, nearly four times faster than the company’s previous fastest model.

That is also about twice as fast as a mainframe system announced last month by Japan’s Hitachi Ltd., which was dubbed the world’s fastest.

Mainframe computers manage huge database networks for government agencies and large corporations.

Industry analysts were skeptical that NEC’s new computer system would help it climb from its current fifth-place ranking in Japan’s high-end mainframe market. The company has about an 8% share of the market in Japan, and its share overseas is minuscule.

“It’s a formidable machine, but I don’t see NEC taking significant market share with it,” said Steve Myers, an analyst with Jardine Fleming.

One problem is that the new machine is incompatible with models made by International Business Machines Corp., the leader in the field. Another is consumer reluctance to buy new systems with different standards unless absolutely necessary.

“Somebody once said that switching mainframe systems is a bit like moving house; by the time you’re done you could lose as much efficiency as you’ve gained,” said Mike Jeremy, an analyst at Baring Securities.

Yet another difficulty is that with other makers bringing out comparable machines, hardware performance may not be the determining factor.

“The real battle for market share is in hiring good software engineers and supporting the product in the marketplace,” Jeremy said. “And NEC has no more leverage in this than IBM Japan or Fujitsu.”

The NEC announcement is one of a round of product unveilings as manufacturers compete for new business in the $20-billion global market for mainframes.

IBM, Fujitsu Ltd. and Fujitsu’s 44%-owned subsidiary, Amdahl Corp., are expected to announce new machines within the next year.