Memory technology set to evolve with DDR2

With so much emphasis placed on processors, memory chips often get overlooked as an integral component of system performance. DRAM (dynamic RAM) vendors will start the transition to a new memory architecture this year that will allow chips to run faster in gaming and multimedia PCs.

Just about every PC sold these days uses DDR (double data rate) SDRAM (synchronous DRAM) in one of four main speed grades. PC3200 memory is the most commonly used memory in performance systems with an effective clock rate of 400MHz, although faster technology exists that has not been ratified by a standards body.

The next step in the evolutionary chain, the new DDR2 architecture, will allow those memory chips to run faster. DDR2 memory will also be used in servers to help boost performance.

DDR2 memory improves the signal quality of data transmissions traveling within a PC, said Dean McCarron, principal analyst with Mercury Research Inc. in Cave Creek, Arizona. Memory chips based on the older architecture could not run much faster than the current speeds without suffering a marked decline in signal quality, he said.

In order to ratchet up memory speeds, chip designers effectively doubled the number of signals the memory chip could process using a technique called differential signaling, McCarron said. They also added on-die termination, which allows the memory chip to absorb more "noise" created by signals as they travel through a system and therefore improve signal quality, he said.

Micron Technology Inc., Samsung Electronics Co. Ltd., Elpida Memory Inc., Hynix Semiconductor Inc.and Infineon Technologies AG are all currently shipping DDR2 memory chips at 400MHz and 533MHz date rates.

PC users won't be able to simply plug in new memory modules to take advantage of the technology, because the modules will require new chipsets. Intel Corp.'s Grantsdale chipset will support DDR2 when it is launched in the second quarter, and Via Technologies Inc. and Silicon Integrated Systems Corp. are also expected to support DDR2 in forthcoming chipsets.

DDR2-400 is not expected to offer a large increase in performance as compared to DDR400, McCarron said. The standard will really begin to shine with later versions that will run at 533MHz and 667MHz, he said.

By 2005, DDR2 prices should be equivalent to DDR400 prices, paving the way for mass adoption, McCarron said.

While DDR SDRAM has been the accepted memory standard for several years, other companies are also working on technologies that will help push the boundaries of performance.

Rambus Inc. has announced a new memory interface called XDR (extreme data rate). It allows for clock rates as high as 3.2GHz, said Rich Warmke, director of product marketing for Rambus.

XDR also uses differential signaling, but uses it throughout its entire architecture, whereas DDR2 uses the technique in only one aspect of its architecture, Warmke said.

Current memory architectures use a technique called multidrop, where multiple memory modules are connected to a single wire, Warmke said. XDR switches to a point-to-point architecture, where each memory module communicates directly with the memory controller without having to share bandwidth with other modules, he said.

Toshiba Corp. and Sony Corp. have licensed the XDR technology, which is expected to make its debut in consumer graphics and networking products, Warmke said. By 2006 or 2007, the technology should be ready for the PC market, he said.

Chip maker Intel also recently presented a paper at the International Solid State Circuits Conference in San Francisco detailing its work on a point-to-point signaling memory architecture.

Intel demonstrated a point-to-point technology that also uses simultaneous bidirectional signaling, where signals can be sent simultaneously in opposite directions down a single wire, said Shekhar Borkar, a fellow with Intel Labs. In a demonstration, the memory interface produced 3.6G bps (bits per second) of bandwidth, he said.

At this point, Intel's technology is only a research project, and any products based on the new interface would be several years away, Borkar said. Intel will submit the technology to the standards community as products near release, he said.

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