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  DDR and RDRAM, an Ongoing Battle 
  Mar 14, 2002, 08:00am EST 

DDR, PC2100 and more

By: Sander Sassen

In our ‘i845D, SiS 645, P4X266, DDR on the Pentium 4 platform’ article we’ve looked at the performance and stability of the various DDR chipsets for Pentium 4 already, but used engineering samples motherboards due to lack of shipping production version motherboards. This naturally meant we didn’t weigh any stability concerns or other issues to heavily as these obviously were still being worked on and should be remedied with the production versions of these motherboards.

Corsair XMS DDR

Fig 3. The excellent Corsair XMS PC-2700 modules we used during our testing. Rated at 333MHz and Cas-2.5 operation.

However during our second round of testing we have used production versions of these motherboards and naturally set out to see whether these stability issues had been fixed and performance might have been improved. Performance seemed to be at the same level as we’ve seen from the benchmarks from our previous article, so we will not be commenting on that any further. Unfortunately we ran into the same instabilities with a number of these motherboards that we’d hoped would’ve been remedied with the production versions. We came across the following:

  • Intel’s i845D chipset was stable throughout all of our tests, when using a maximum of two banks of PC2100 DDR up to 1GB, which is the maximum allowed size according to the chipset’s specifications. The i845D ran all modules we tested at their rated Cas-2 speeds without any problems. Running at PC2700 was also possible while remaining stable, but we were only able to use a Cas-2.5 setting for the DIMMs.
  • SiS’ 645 was stable when two banks were used, again using a maximum of 1GB of PC2100 DDR running at Cas-2. When using PC2700 DDR two banks could be used also, but only at Cas-2.5 which meant only a small performance benefit over PC2100 at Cas-2.
  • SiS’ 645 was not able to run three banks at speeds over PC2100 at Cas-2.5 without becoming unstable. This means that the maximum performance is only available with two banks at PC2700, and a maximum of 1GB of memory.
  • Via’ P4X266 was stable when two banks of PC2100 DDR at Cas-2 were used, three banks could be used also, but three banks of PC2100 was unstable at Cas-2 and Cas-2.5.
  • Via’ P4X266 runs three or four banks of PC1600 at Cas-2.5 and we used up to a total of 2GB of memory. This was the only configuration that was stable throughout our testing, unfortunately PC1600 at Cas-2.5 is rather slow compared to today’s standards.
  • Via’ P4X266 was unable to run stable at PC2700 speeds at any Cas-setting for the DIMMs with any number of DIMMs.
  • Intel’ i850 was stable when running two or four 256/512MB RIMMs at PC-800 and PC-1066, yielding a total of up to 2GB of memory. Unfortunately PC-1200 was only stable when two 256MB RIMMs were used, which isn’t suprising as we’re running 50% over the chipset and RIMM module specification.
To summarize our findings it turns out that PC2700 is only viable on the SiS 645 chipset running at a Cas-2.5 setting, even with Corsair’s excellent PC2700 DIMMs, which doesn’t really provide enough performance benefits over PC2100 running at Cas-2 to convince us that PC2700 is indeed so much better than PC2100. PC2100 DDR on the Pentium 4 platform is only a valid solution for users that don’t require more than 1GB of memory or users that are willing to sacrifice performance in order to run up to 1.5GB of memory on SiS 645 chipset. The SiS 645 was the only chipset able to run three PC2100 modules at a Cas-2.5 setting, Via’ P4X266 was not stable at these speeds and had to revert back to PC1600 with three and four modules to regain stability.

Rambus’ RDRAM in combination with the i850 and Samsung’ PC-800 RIMMs continues to impress as it is free from any instabilities up till PC-1066 speeds with a total of 2GB of memory, twice that of most DDR chipsets. However PC-1200 speeds could only be attained with two 256MB modules which isn’t surprising as we’re running both the chipset and the RIMMs 50% over specification.

1. Introduction
2. RDRAM, PC-1066 and PC-1200
3. DDR, PC2100 and more
4. Benchmarks and more
5. Conclusion

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