"We've been talking about Rambus a long time, and it was looking like it would be the foremost architecture," said Samuel Rogan, AMD's marketing manager for Japan and Korea. "There will be a time when that will happen, but probably not until the end of 2000 or 2001."

The problem with Rambus is that the extra cost, which Rogan estimates will be $60 to $80 per motherboard, is hard to justify given that SDRAM — particularly DDR — will provide equal or better performance bandwidth, he said.

During its presentation on the Athlon processor here, AMD showed a slide indicating that 100-MHz double-data-rate SDRAM with a standard 64-bit memory bus will provide 1.6 gigabytes/second of bandwidth, equal to a 400-MHz (800-MHz effective) Rambus DRAM running on Rambus' proprietary 16-bit serial bus. DDR SDRAMs with a core frequency of 133 MHz (266-MHz effective) will ratchet up memory bandwidth to 2.1-gigabytes/s, according to the company.

"Rambus boasts higher frequency on data transfers, but because of the narrower pipe they do not get the same data throughput as you do with DDR," Rogan said. "Since DDR has comparable or better performance than a Rambus solution at a better cost, the motherboard guys like it and the DRAM manufacturers don't have to retool."

Rambus is expected to hit the market next month with the introduction of Intel's Camino chip set, which will include a Rambus interface and is expected to support 4x AGP. Depite a delay in the chip set introduction and the high cost of Rambus DRAM, Intel continues to promote Rambus as the next mainstream memory technology after PC100, though more recently the company said it will consider introducing a PC133 chip set as well.

By contrast, AMD will look to follow third-party chip set suppliers and memory manufacturers that are offering a wide choice of memory types. For example, the new Apollo KX133 chip set from Via Technologies Inc. supports 133-MHz SDRAMs, 4x AGP as well as the 200-MHz front-side bus geared for Athlon.

Just what will PC makers get for moving to a faster processor bus and SDRAM? According to Asao Ishizuka, a long-time industry consultant who tests motherboards and writes for Nikkei Business Publications, making the switch from a system with a 100-MHz front-side bus and PC100 SDRAMs to a system with a 133-MHz front-side bus-capable chip set and 133-MHz SDRAMs increases memory subsystem performance more than 20 percent.

What's more, using a 133-MHz variant of SDRAM from NEC, known as Virtual Channel Memory, with a 133-MHz front-side bus yields a memory subsystem performance increase of more than 50 percent over systems with PC100 SDRAMs and a 100-MHz front side bus, Ishizuka said.

(Ishizuka's results were based on a Stream for DOS benchmark. The test system used a First International Computer (FIC) motherboard with a 600-MHz Pentium III CPU, 128 Mbytes of RAM and Via's Apollo Pro 133 chip set. Both the PC133 and PC100 CAS-2 double-sided dual-in-line memory modules were manufactured by Micron Technology. NEC provided the Virtual Channel Memory module.)

Though he hasn't completed tests for non-Intel chip sets capable of 4x AGP using the faster DRAMs, Ishizuka said he expects a substantial improvement for graphics and game applications. Presently, PC100 SDRAM provide sufficient memory bandwidth for 2x AGP, so using faster memory with 2x AGP chip sets provides only negligible performance gains, he said.

"You can gain a lot with PC133 and you can gain more with Virtual Channel, as expected," Ishizuka said. "Overall system performance for running traditional applications like Excel and word processors doesn't gain much. But AGP 4x demands a very high level of memory bandwidth for running graphics and games, and I expect it will show better gains than a system which uses AGP 2x."

Ishizuka said he has done tests on Intel's Camino chip set, which will support a 133-MHz front-side processor bus, 4x AGP and Rambus DRAMs, but declined to disclose the results due to a non-disclosure agreement with Intel.

As for DDR chip sets, AMD's Rogan said he expects the first to be available by early next year. DRAM vendors have been sampling DDR SDRAMs for several years, and are gearing up to make the shift to so-called PC266 DRAMs, which are DDR SDRAMs with a core frequency of 133-MHz that transfer data on both the rising and falling edge of the clock. Hitachi, for one, recently said it will start sampling a 256-Mbit DDR device with a 133-MHz core frequency that provides a peak data bandwidth of 2.1 gigabytes/second, though the device is aimed high-end servers and workstations. Joint Electronic Device Engineering Council, the standards body, is also working on completing a final spec for DDR by September.

"The memory guys are ready to go; it's a question of the chip set," Rogan said.

Via, for one, intends to come out with a DDR-enabled chip set "early next year" that will support the PC266 speed grade, said a company spokesman in Taipei.

One unknown, however, is Via's legal scrap with Intel, which revoked the Taiwainese company's P6 license last month and filed a lawsuit to stop the company from selling chip sets based on Intel's P6 bus.