Industry sources said the virtually unknown restriction explains why Intel recently licensed patents for chip set support of DDR memories to Via Technologies Inc., Acer Laboratories Inc, and Silicon Integrated Systems Corp. (SiS) in Taiwan. The pacts allow these three companies to offer DDR chip sets for Intel's Pentium III and Celeron processors.

An Intel spokesman in Santa Clara denied that the company's DDR chip set deals had any connection with Intel's own Rambus licensing agreement. He agreed, however, that independent chip set suppliers could fill a void for DDR support in PCs with Pentium III and Celeron processors, since Intel has no double data rate products.

DDR chip sets are becoming a paramount concern for Intel, since later this year Athlon processors from archrival Advanced Micro Devices Inc. will be supported by a bevy of new double data rate chips. Unable to sell any of its own DDR chip sets for PCs, Intel has been forced to rely on other suppliers to provide logic/memory controllers to compete against AMD's high-end central processor, according to sources.

Two obscure clauses in Intel's 1997 licensing pact with Rambus allows the Mountain View, Calif., memory design company to terminate its agreement with Intel, if the microprocessor giant introduces chip sets with DDR capabilities supporting memories other than the Direct Rambus DRAM in the 2000-2002 time period.

Rambus can void the license if "Intel communicates to any of the then current top 10 DRAM manufacturers that Intel has plans to support, as the primary DRAM for PC main memory applications for the years 2000, 2001, and 2002, any new interface other than the (Direct) Rambus Interface," according to a clause in the 1997 agreement.

The license can also be canceled if "Intel does not represent to Rambus that the (Direct) Rambus DRAM will be the primary DRAM for PC main memory applications for the years 2000, 2001, and 2002," the pact adds. An Intel DDR chip set would fall under the "new interface" ban that targets any "DRAM interface which provides greater than 1 Gigabytes/second bandwidth."

There is a now unlikely DDR escape hatch for Intel in the 1997 agreement--if at any time before 2003 "the cost of the (Direct) Rambus DRAM is within 5% of the cost of 100-MHz 4-megabit-by-16 SDRAM manufactured on the identical process." With production costs of Direct RDRAM chips now twice as much as costs for synchronous DRAMs, this escape clause allowing Intel DDR chip sets is far from becoming effective.

The clauses -- 9.2(b)(iii and iv) -- are contained in Rambus' initial stock registration statement S-1 Amendment 4 filed with the Securities and Exchange Commission on April 29, 1997.

Intel in June was able to introduce its 815 series chip set supporting 133-MHz SDRAMs under terms of the pact, which allows the firm to make "evolution of (existing) main memory interfaces on chip sets." The 815 is viewed as a more powerful successor to widely popular Intel 440BX SDRAM chip set and could deter the transition to Direct RDRAM for mainstream desktop PCs.

Another independent PC logic chip supplier, ServerWorks Inc. of Santa Clara, is also making DDR chip sets for Intel's next generation "Foster" and "McKinley" processors for servers. Intel might be able to market its own DDR chip set for servers under its Rambus agreement, which bars the company from offering double data rate support specifically for personal computers. The issue here is whether servers are considered different from powerful PCs.

The market will be watching very closely what approach Intel takes on any DDR support for its upcoming next-generation Willamette desktop central processor unit. Intel so far is adamant that Willamette will use its Tahama chip set, which only supports Direct RDRAM. That meets the terms of the Rambus agreement, which would block any Intel DDR chip set for the Willamette CPU. Rumors have been rife that Intel is quietly developing a Willamette DDR chip set, but clearly such a controller would fall awry of the 1997 Rambus pact.

The Willamette DDR question comes to the fore in Intel's current high-end MPU battle against various high-performance AMD Athlon versions, which will support DDR. Separately, Rambus in Mountain View bolstered its high-speed memory by announcing this week that more than 100 products, using Direct RDRAM, are now available from PC and consumer product OEMs.

Rambus said the number of systems using its memory format was twice that of products using RDRAM when a similar market survey was conducted in April. Among the PC makers selling Direct RDRAM-enabled products are Compaq, Dell, IBM, Hewlett-Packard and Sony, according to Rambus officials.