Los Altos (CA) - In an interview, Rambus director of product marketing Rich Warmke told Tom’s Hardware Guide that his company’s patented micro-threading technology may be applied in the not-too-distant future to a future version of its XDR DRAMs, and in so doing accelerate the performance of its memory even further.

"To date, we haven’t announced any specific Rambus products that have incorporated micro-threading," Warmke said, "but you can probably make a safe assumption that, sometime during the near future, a next generation product from Rambus will likely incorporate it."

XDR memory uses, among other advances, differential signaling - the use of two signals to represent a binary value rather than just one. This way, explained Rambus’ senior principal engineer Dr. Steven Woo, factors such as increased signal noise which occur when memory bus speeds are accelerated, are cancelled out since noise tends to affect both signals in a differential array equivalently. Dr. Woo characterizes advances such as differential signaling as "signal innovations ;" whereas micro-threading is a logical innovation, affecting the logical dynamics of how memory is accessed.

The need for micro-threading, explained Dr. Woo, emerges from an unwanted side effect of the evolution of DRAM : the growing disparity between the interface frequency and the rate at which chunks of data can be polled from memory. "It turns out that DRAM cores are not very fast components," he said. "So let’s say the interface is trying to signal at 16 times the speed of the DRAM core. The only way you can really deal with this is to pull 16 times more information out of the core every time you access it." As the mismatch grows over time, added Dr. Woo, the size of the average memory fetch increases.

This mismatch is a fact of life, confessed Dr. Woo ; but the objective of micro-threading is to compensate for it. DRAM typically is divided into halves or quadrants, so micro-threading enables each of these quadrants to be treated independently, enabling separate but parallel fetches of not-necessarily-related elements of data. One example of such data elements, he told us, is a mesh of triangles in a 3D graphics application, from which individual triangles may be distributed among independent memory quadrants. "If I can do all four of those simultaneously," Dr. Woo said, "I can still get the bandwidth, because the quadrants are relatively independent of each other ; but in the grand scheme of things, I still get the very large bandwidth that I want, because I can do all four of these things in parallel. The data from each quadrant comes out on different pins of the DRAM."

Yesterday, Rambus announced that it has licensed its XDR memory interface technology, called "XIO cell," to IBM for use in that company’s 90 nm Cu-08 ASIC fabrication process. In a press release, the company characterized IBM’s interest in XIO cell "for high-performance consumer applications utilizing their state-of-the-art 90 nanometer (nm) ASIC process." Last February, IBM - along with design partners Sony and Toshiba - revealed general implementation details of their Cell processor (not to be confused with XIO cell), which utilized a different version of XIO cell licensed earlier to IBM through Sony and Toshiba. Yesterday’s license applies to a different market - "IBM’s ASIC customer base on the 90 nm process," as Rich Warmke told us.

"The XDR memory interface is applicable to consumer electronics-type applications," said Warmke, "such as game consoles, but also other applications such as DTV, PC graphics, imaging, and networking applications, and potentially in the future, performance computing systems. The fact that IBM has taken a license to have this cell available to their ASIC customers speaks to the fact that there are additional customers that are looking to use XDR memory for their next-generation products."

Warmke added that the XIO cell already licensed to IBM will enable its Cell processor to interface with four XDR DRAM modules in Sony’s next-generation PlayStation 3 game console. Over the next few years, conceivably, future XDR memory utilizing Rambus micro-threading technology may be a candidate not only for accelerated game consoles, but also to replace GDDR memory in graphics cards. Rambus’ engineers also foresee applications in network switching devices, where small packets are temporarily stored while forwarding routes are made way for them.

Meanwhile, Warmke stated, Rambus intends to offer its micro-threading technology as IP for licensing to any manufacturer of DRAM products - including those with whom the company is currently tied up in litigation. "We announced micro-threading as a technology that can be applicable to any memory type. So you can almost view it as an ingredient technology. You can take any existing DRAM core and turn it into a micro-threaded core by implementing this technology."