As mentioned the i820 wasn't really living up to expectations in the performance department, even though the RDRAM memory offered an, at that time, impressive 1.6Gb/s bandwidth. Much debate started about the RDRAM having higher latency than SDRAM, consuming up to ten times as much power as SDRAM and being overly expensive for the average user. All the points raised were more or less tackled along the way, the only thing that remained was the higher cost of RDRAM, something which didn't do wonders for the price/performance ratio, simply because the i820, and I'll put it bluntly, was handicapping the RDRAM.
Fig 2. Intel i820 chipset featured on an Asus motherboard. Despite the fact that Asus had built a very fast motherboard around the chipset it offered little improvement over the reigning champion, the Intel 440BX.
Handicapping? Indeed, simply because the i820 chipset used a 100 or 133MHz system bus to the main memory meant that the RDRAM was never able to perform as expected, the system bus and the overall chipset bandwidth quickly became the bottleneck, rather than the memory. A rather big oversight from the people at Intel, as Rambus itself didn't have anything to do with the functional design of the actual chipset, they just provided the technology for the memory interface. It is sad to see that very few journalists identified this cause for the RDRAM memory not performing as expected, they'd rather picture RDRAM as a overpriced, under-performing and generally a bad investment. We're glad to see that Intel didn't repeat on its mistake with the i850 and i860 chipsets as both these chipsets show what RDRAM is really capable of. The quad-pumped 100MHz system bus, equaling 400MHz in total, means that the RDRAM modules are no longer handicapped by the system bus bottleneck and finally show some of the bandwidth they're capable of delivering.
Fig 3. Intel i850 chipset as featured on the Asus P4T-E as used during our testing, featuring the NetBurst architecture and dual channel RDRAM with 3.2Gb/s of bandwidth.
Part of the performance of the Pentium 4 is due to the impressive bandwidth of the dual channel RDRAM. Therefore it came as no surprise that the Pentium 4's SDRAM chipset, the i845, offered nothing more than a low-cost solution, it is not to be considered a viable alternative to the i850 chipset in terms of performance. Upon looking at the feature set of the i845 and the benchmarks one thing is obvious, if a customer would want to have similar performance out of his i845 chipset as with a 1.5GHz Pentium 4 with RDRAM he would need a processor running at a 2GHz or higher clockspeed. So what would you prefer to do, buy a cheap motherboard and cheap memory and then pay a price premium for the processor or rather go with the i850 platform and RDRAM memory from the start?
But overall it is good to see that RDRAM can now finally deliver on its promises with the i850 and i860 chipsets and that RDRAM has been able to prove its worth with the Pentium 4 and the Pentium 4 Xeon. From a bandwidth and overall performance perspective it is save to say that DDR didn't do as well. The performance deltas offered by today's DDR systems are finally showing some of the performance initially promised back in 1996. It is however strange to see that none of the journalists that were quick to condemn RDRAM have addressed this issue as they should have.