Why did my processor speed change after I added memory?

Q  I have a Windows 7 (64-bit) PC with an Intel i7 920 processor with a Gigabyte GA-EX58-UD5 motherboard. I recently upgraded the 6GB of Crucial memory with another 6GB Crucial Ballistix 3 Channel Kit.

When I refreshed the Windows Experience Index, my processor score had dropped from 4.7 to 4.2, and my memory score had dropped from 7.2 to 6.2. Can you explain why?
Stephen Williams

A  The Windows Experience Index is not an accurate benchmarking tool, so it’s worth using something designed expressly for this purpose to assess the PC’s performance. Sisoft Sandra Lite is a free download and has a range of built-in benchmarking tools, including memory-specific tests.

We suggest running the benchmarks first with just the original 6GB of memory installed, then just with the new 6GB of memory installed and then one more time with all 12GB installed. Now compare the results.

That said, there does appear to be a limitation with the Intel X58 chipset used on the Gigabyte GA-EX58-UD5 motherboard (and those from other manufacturers).

As the Gigabyte list of supported memory mentions, 1,600MHz DDR3 memory is only supported for one Dimm per channel, which is what you originally had with the three 2GB Dimms. With two Dimms per channel – ie, the six 2GB Dimms now installed – the speed drops to 1,066MHz, which would explain the lower Windows Experience Index score.

Similarly, addressing 12GB of memory places extra demands on the PC’s processor, which would also account for its lower score. So, it looks like you have a choice between a very fast PC with 6GB of memory, and a slightly slower one with 12GB.