Originally Posted by Blameless
Yes it makes a difference, and no the memory in each channel doesn't have to be identical (you just need to have clocks, timings, and voltages that are stable for all memory involved).
With different amounts of memory in each channel, you limit yourself to dual-channel asymmetric mode. As you have it now, only the first 8GiB of memory is actually going to perform like dual channel. Once those first 8GiB of addresses are used up, the remaining 4GiB can only function in single channel (because they have no corresponding addresses in the other channel).
Chances are this will rarely be an issue, but when you have the capability of making each memory channel symmetrical, and have full dual channel over the entire amount, there is zero
reason to not do so.
This is from an ASUS AM3+ mobo manual, but it applies to all Phenoms:
There is a bit of misconception here. Interleaving/flex memory would apply with 3 DIMMs. The user in question is using 4 DIMMs for 2 DIMMs/channel operation. It's a bit hard to explain but I am going to attempt anyway:
- Dual channel has to do with having a pair DIMMs spread over two channels (channels: pathways between the memory slot and memory controller), to allow for increased throughput from each DIMM. There is, however, the option of running dual channel assymmetrical. In asymmetric
correction-symmetric dual channel with 3 DIMMs, one pair can be split over two channels; the other third DIMM cannot, but it has the same amount of memory as that pair. Example (all examples use a 1-2-1-2 channel/RAM slots layout): 2GB + X + 2GB + 4GB. It will run with increased performance over single channel but reduced performance over dual channel symmetrical.
- In Interleaving/asymmetric dual channel mode, one pair can be split over two channels; the other cannot, and it does not have the same amount of memory as that pair. i.e. 2GB + 2GB + 2GB + X, 4GB + 4GB + 2GB + X. When the first two paired DIMMs are activated/used, they will be mapped in dual channel. When the extra memory is used above that, the entire setup will have to reverse to single channel. It also works with two DIMMs; in configuration 4GB + 2GB + X + x, 2GB of the 4GB DIMM is mapped with the other 2GB DIMM as dual channel. The remaining memory is mapped at single channel.
- If you have two pairs of DIMMs spread over two channels, even if the two pairs of DIMMs have different sizes (i.e. 2GB + 4GB + 2GB + 4GB) it will run in symmetric dual channel mode as usual.
Source: Intel/Kingston spec sheets released in 2003 with the unveiling of dual channel technologyEdited by xd_1771 - 8/19/11 at 12:27pm