Analysis: Rambus readies four-channel DRAM

Rambus readies four-channel DRAM
By Jack Robertson, Semiconductor Business News
February 11, 2003 (12:47 p.m. EST)
URL: http://www.eetimes.com/story/OEG20030211S0025

Rambus Inc., once a strong memory partner of leading processor maker Intel Corp., will soon become a competitor in its effort to support next-generation workstation and high-end desktop processors.

The switch comes as Intel starts to phase out its 850E chipset -- the last to support Rambus DRAM -- and moves in the second half of the year to dual-channel DDR SDRAM.

Intel confirmed that its upcoming 875 chipset, the Canterwood, will support dual-channel DDR1/333 and DDR1/400 for workstation and high-end processors using a new 800-MHz frontside bus (FSB).

Analysts said Intel has no plans at this time to develop a new RDRAM chipset as a follow-on to the 850E. An Intel spokeswoman would say only that the Santa Clara, Calif., company would continue to design its products to be compatible with "whatever memory our customers want."

"Intel has cast its lot with two-channel DDR, and the company has a lot of market power to make that stick," sai d Lane Mason, a memory analyst at Denali Software Inc., Palo Alto, Calif. "There's always a large group of systems customers who will want to follow the Intel roadmap."

Dean McCarron, an analyst at Mercury Research, Scottsdale, Ariz., said the battle over whether customers will choose RDRAM or DDR SDRAM in Intel-based computers, "is centered in a niche high-end market. It won't have a whole lot of impact in the overall PC market."

Rambus believes its memory and chipset partners will compete in the post-850E market with a new chipset, the SiS R659 from Taiwan's Silicon Integrated Systems Corp., which is expected to enter production in the second half of this year.

The chipset will support a new four-channel memory represented by existing RDRAM speed grades and up-coming 1.2-GHz RDRAM chips, said Steve Tobak, senior vice president of worldwide marketing for Rambus, Los Altos, Calif.

"We expect volume production in the second half on 1,200-MHz RDRAM, with a memory bandwidth of 9.6-Gbytes/s," T obak said.

Since last year, SiS has offered a chipset that supports 800-MHz and 1,066-MHz RDRAM and competes with Intel's 850E. When Intel switches to dual-channel DDR, "it will be a boon for SiS because it will have the RDRAM market [for Intel processors] to itself," said Michael Cohen, director of research for Pan American Securities LLC in Fremont, Calif.

Despite Intel's plans to field the DDR-compatible 875 chipset, Tobak said Rambus continues to have "an excellent relationship with Intel in the PC area. Intel also uses RDRAM as the memory for its network processor and has adopted the [Rambus] Raser serial link for its future Ethernet applications."

Race to continue

The ongoing contest between DDR and RDRAM will result in a horse race in which each architecture is expected at various points to claim the title of the industry's highest-performing memory.

Samsung Electronics Co. Ltd., which manufactures both DDR and Rambus chips, said the introduction of dual-channel DDR1/333 in the first half of 2003 will provide a temporary lead over the data speeds of RDRAM.

Jim Elliott, senior DRAM product marketing manager at Samsung Semiconductor Inc., San Jose, said dual-channel DDR1/333 would offer a 5.1-Gbyte/s data rate, compared with today's 4.2-Gbyte/s dual-channel, 1,066-MHz RDRAM.

"RDRAM regains the bandwidth lead when the four-channel, 1,066-MHz becomes available in the second half of this year with an 8.4-Gbyte/s bandwidth," Elliott said. "When the four-channel, 1,200-MHz comes on the market, the RDRAM bandwidth lead is even greater at 9.6-Gbytes/s."

Pan American's Cohen said the speed advantage of RDRAM could convince Intel to design the chips back into its PC roadmap, noting that Intel last fall reversed itself by adding 1,066-MHz RDRAM support to the 850E after originally declining to upgrade the chipset.

Multiplier mismatch

However, the frequency-multiplier mismatch between 1,066-MHz RDRAM and Intel's new 800-MHz FSB is a challenge when competing a gainst the frequency multiplier of DDR1/400, said Jim Sogas, vice president of sales and marketing for Elpida Memory (USA) Inc., Santa Clara, which also makes both memory types. Data throughput is more efficient when the memory-clock speed is a multiple of the processor FSB, Sogas said.

A Rambus spokeswoman countered this observation by noting that, "the four-channel chipset includes logic gears that work with 800, 1,066, and 1,200-MHz RDRAM. Our architects have solved synchronizing the front-side bus to all of these frequencies," the spokeswoman said.