Nexgen has begun shipping chips that offer performance comparable to Intel's Pentium microprocessor.

Pacific Microsonics began shipping chips earlier this year, and there are now 36 makers of CD players using the decoder.

Still, under the ruling, Advanced Micro is free to ship existing chips to customers through Jan. 15, thus sparing the company a financial penalty for the rest of the year.

Advanced Micro will not ship 486-compatible chips in volume until late this year or early 1993.

And today, Paul P. Castrucci, the plant manager at the Burlington semiconductor operations, said the company had already shipped megabit chips "in the millions" to its only customer: I.B.M.'s computer manufacturing plants.

Still, Cyrix to some extent is in a better position than Advanced Micro, because it is currently shipping Pentium-equivalent chips, analysts said.

Until recently, I.B.M. shipped chips to Japan only for inclusion in computers that it builds there.

The memory chip currently in broad use in most computers is the 1-megabit, although all of the major Japanese manufacturers, along with American companies like I.B.M., are now shipping 4-megabit chips as well.

New Chips From Advanced Micro Advanced Micro Devices plans to announce that it has begun to ship chips based on a process that is being used to build the next generation of processors.

Advanced Micro, which has had trouble shipping faster chips, said last month that it would report a second -quarter loss of about $200 million.