Update 6: A-Data and Corsair Miss the 1000 MHz Target
We decided to conclude our live memory stress test with a head-to-head comparison between A-Data and Corsair DDR2-1000 DIMMs. Both test systems increased the Front Side Bus by one Megahertz every 50 minutes, which had the stress test run during the entire weekend. The memory underwent an intensive memory test after every increment, which would crash the system if the memory clock speed does not run reliably.
Corsair rated its XMS2-8000UL parts to run at 500 MHz (DDR2-1000 speed), CL5-4-4-9 timings and 2.2 V. A-Data is more conservative by staying with relaxed CL5-5-5-15 settings, but it also recommends the same memory voltage of 2.2 V, which we applied. We also decided to run the most conservative timings of CL5-5-5-15.
The outcome of this stress test run was surprising, because the Corsair test system crashed at 456 MHz memory clock. This equals DDR2-912, which is 8.9% below the rated speed of DDR2-1000. A-Data’s memory was able to support up to 476 MHz, which corresponds to DDR2-952. But this is still well below the DDR2-1000 specification ! However, both memory products were capable of running at their rated speed on an Asus P5WD2-E, which shows that you should pay close attention to the motherboard recommendations of your favorite memory vendor.
We took this CPU-Z screenshot prior to running the DDR2-1000 stress test. It proves that the test systems are capable of supporting higher Front Side Bus and processor clock speeds than we required to push the A-Data and Corsair DIMMs to their limits.
What is the reason for this rather large difference between the manufacturers’ specifications and the real-life memory clock speed ? Both systems were identical and were able to reach higher Front Side Bus and processor speeds than required in the stress test : 373 MHz FSB and 4.46 GHz processor clock are the limits, and these are suitable to push a memory product well beyond the 1,000 MHz line.
It seems to be a problem with the Gigabyte motherboard or its current BIOS version, because we did not encounter problems on an Asus P5WD2-E a couple of weeks ago. But from our point of view this does not really matter. If you spend a lot of money on a premium-class motherboard and state-of-the-art overclocking memory, you will expect it to work. We also need to point out that DDR2-1000 memory is an unlucky choice. The 975X provides a DDR2-888 setting, which will force you to overclock the Front Side Bus in order to reach DDR2-1000 memory speed. The alternative is the DDR2-1066 option, which requires even faster memory. At the same time, both settings are well above the chipset specification, which allows for a maximum memory speed of DDR2-667.
We do not recommend to buy a high-end memory product if the advertised clock speed is way beyond the current memory specifications. Those high-end DIMMs are scarcely available and very expensive, and only few of them are validated for a wide platform basis. If you still decide to go for the highest-end you should bear in mind that it might not work the way you want it.