i7 Memory Controller Limits

Question

Intel's specs say that the 2670QM's memory controller supports 16GB of memory, but they add the qualifier that it is dependent on memory type. Am I correct in assuming that 16 is the highest possible maximum, and not the guaranteed maximum? What happens if I install more than 16? I'm seeing reports of people installing 48GB on consumer i7 setups which are specced at 24GB and having them work, so I'm somewhat confused.

Answer 1

Am I correct in assuming that 16 is the highest possible maximum, and not the guaranteed maximum?

It is the maximum amount of memory that Intel guarantees will work.

There is a lot of speculation why Intel hasn't validated larger memory configurations. One theory is that the memory wasn't available at the time they did the validation. Another theory is that Intel wants to segment the market and direct people with greater needs to more expensive products.

Another theory is that these implementations don't quite meet Intel's strict criteria for stability, making using more memory somewhat akin to overclocking. This is somewhat plausible because Intel's testing makes the worst possible assumptions for every possible parameter (temperature just inside limits, voltage just inside spec, noise the most allowed, everything right at the edges of tolerances, and so on) so you can have configurations that fail Intel's testing but are 100% rock solid.

Answer 2

Just looking at the current lineup of Alienware laptops, you can configure successfully with Windows 7 Ultimate 64bit, 32GB RAM, and the 2670QM processor. Other configurations like Windows 7 Home 64bit, 32GB RAM and the 2670QM processor returns an error. Therefore, since it looks like they are doing compatibility checking, I would assume to answer your question that it is possible.

Answer 3

Sandy Bridge can do 16GB of regular DDR3, or 32GB ECC. Due to extra pins needed for ECC, the motherboard has to support it. Since Nehalem the memory controller is in the CPU itself, so it's largely up to the CPU what's supported. Also, 8GB ECC sticks are expensive, comparatively to their 4GB counterparts. Intel likes us to believe that only Xeon's come with the 32GB of RAM support, but that's not exactly the case.