X-bit labs

Kentron’s QBM Calls for DDR2.

Category: Memory

by Anton Shilov

[ 06/29/2004 | 10:55 AM ]

Kentron Technologies, a company that once tried, but failed, to bring an innovative memory technology that could enable high-bandwidth using low-priced DRAM chips, has come up with the idea once again, but this time the approach will include DDR2 SDRAM and additional logic to maintain compatibility with chipsets that do not originally support QBM.

Quad Band DRAM allows to double memory sub-system’s bandwidth using the widely-spread DDR SDRAM chips. Modules, that correspond to QBM standard make use of ordinary memory chips but add a special PLL (switch) to allow half of the chips to work at 90 degrees displaced frequency, hence, data becomes available almost two times more frequently compared to ordinary modules. Basically, such way of functioning resembles a 128-bit memory module with a pair of 64-bit channels that switch, in turns, one over another.

The peak bandwidth of such RAM system can be up to 4.2GB/s when using ordinary 266MHz memory chips (PC2100), the main advantage of this technology is its presumable cost-efficiency. Since QBM technology does not require any additional signaling, QBM memory modules can maintain compatibility with widely available memory slots, such as those used for DDR or DDR2 memory. Still, QBM requires chipset support, which, in the past, lead to Kentron’s flop in the market as VIA Technologies, the only maker of chipsets who planned to support QBM, dropped the idea of Quad Band Memory-supporting core-logic.

In an interview with Engineering Times web-site Badawi Dweik, Kentron’s applications engineering manager, said the company was planning to release QBM-2 specification and modules in the first half of 2005, bringing high-speed DDR2 800MHz options into the market. In order not to depend on third-party chipset makers, Kentron plans to install supporting logic straight on memory modules.

“Having extra logic to implement into the memory controller limited us to the memory controllers that supported you, which was one. In order to have broad acceptability, we want the user to make the decision rather than the chipset product group,” Kentron’s spokesman said.

While additional core-logic and PLL chips increase the cost of memory modules, Kentron Technologies believe that low-cost memory chips that provide high bandwidth thanks to QBM technology will compensate the additional costs. Furthermore, once Intel implements its FB-DIMM strategy, conventional memory modules will also get additional logic onboard, which will erode the price difference with QBM-2 modules.

Currently, Kentron designers are completing timing interfaces among the chipset, switch and memory, as well as defining component specs for the switch and controller logic.