Today’s quality top end gaming systems come standard with 2GB of memory, but many are even opting to go with 4GB. From our previous latency testing we knew that 2GB of memory can do CL3 with super tight timings of 3-3-3-8 1T at 800MHz on Corsair’s latest PC2-6400C3 modules, but can the modules do it at 4GB?
To answer this question we used four 1GB modules of Corsair’s PC2-6400C3 to hit 4GB of system memory and then pushed the timings again to see how the memory controller does.
After installing the 4GB of memory in the ASUS M2N32-SLI our system would not post and after talking with Corsair about the issues it turns out our pre-production board works great at typcial settings, but when it comes to overclocking and tight timings our revision was not going to cut it. If you own the ASUS M2N32-SLI with the revision number 1.02 don’t be suprised if you can’t do what we are about to do. With revision 1.03 and newer boards ASUS has fixed the issues and it can do CL3 at 4GB. Using the Foxconn C51XEM288 we were able to start up the system with 4GB of memory installed.
At first our system was unstable at 4GB, but after bumping the memory voltage from 2.2V (Corsair’s Suggested Voltage for 2GB) to 2.425V our system was rock solid. Since anything over 2.4V tends to get the memory really warm we suggest using active cooling to make sure the memory does not get damaged. We used a single 80mm case fan above the memory and it seemed to do the trick just nicely.
With no overclocking on the system and running 4GB of memory on our AMD AM2 4800+ processor we were able to get over 9GB/second of throughput on the test system. We were unable to run anthing tighter than 3-4-3-9 2T and even went up to 2.5 Volts on the memory trying to get the Command Rate down to 1T instead of 2T without success. With 2GB of memory we are able to hit 3-3-3-8 1T, while with 4GB we were limited to 3-4-3-9 2T. Still impressive that 4GB of memory at agressive CL3 timings is possible.
So to anwer the question about 4GB of low latency memory on an AMD AM2 memory controller — It is possible, but more than 2.4V is required and a command rate of 1T seems to be out of the question. Let’s take a look at performance numbers at 4GB versus 2GB.