X-Box and DDR

FiringSquad: Why is the X-Box planning to use DDR SDRAM instead of RDRAM?

We believe that, over the life of any Internet Appliances, the Rambus solution will be the most cost-effective solution because of its low component count, lower cost of implementation, low memory granularity and high memory bandwidth.

At the system level, the reduced pin count offered by RDRAMs results in fewer traces to route on the motherboard, fewer motherboard layers, and the ability to scale bandwidth by adding channels in parallel. These features allow price and performance to be balanced to meet the needs of a particular system. As computing systems continue to undergo greater levels of integration, the high bandwidth and low latency of RDRAM will enable new computing paradigms or unified memory architecture (UMA) systems.

As demonstrated by the PlayStation 2, the Rambus solution provides significant cost reductions to meet the low system price criteria. Toshiba supplies the controller and the RDRAM memory as a system solution. Toshiba has developed and produced Rambus ASIC and RDRAM products for many years. Their system solution is in production now and delivers an unmatched 3.2GB/sec performance with the fewest component count, the fewest controller pin-count and a simplified board layout. From the start of production, the RDRAM component price premium is more than offset by the board level cost savings that the Rambus solution helped achieve.

In the case of the X-Box, Nvidia who will supply the graphics controller may have selected DDR SDRAM because it has recently developed a DDR-based controller for other applications. Their decision may have been influenced more by the schedule and available engineering resources than performance and cost of implementation.

FiringSquad: How does Rambus perceive DDR?

Microprocessor speeds are increasing faster than ever. The latest performance benchmarks put RDRAM-based Desktops and Workstations at the top. With GHz+ systems and multi-channel RDRAM implementations coming in the future, the Rambus advantage will continue to grow.

As for DDR, it is late to market, having been first announced in '96, it's not evolutionary because it requires a different motherboard, and it will carry a premium based on market supply/demand dynamics.

FiringSquad: What does Rambus thinks about Bert McComas' DDR system performance report?

Since DDR systems are not in production, we are unable to verify any performance results, and hence we are not able to comment on Mr. McComas' report.