I want to mix some RAM sticks: Actually I have 2 DDR3 sticks x2 GB (on slots 1,3 to work in Dual Channel – an they are working, if believe to CPU-Z tool). I want to put in other 2 slots (2nd and 4th) other 2 sticks each of 4 GB with the same frequency and timing, but somewhere I read that mixing sizes may affect (disable) such features like "Dual Channel" and "Memory Interleaving".
"Dual Channel" is known (for me) feature, what about "Memory Interleaving" and it will be affected in above described case?
Best Answer
Here's a wiki on memory interleaving, but to directly answer your question; yes, mixing memory types/speeds/etc will result in slower memory timing speeds (lowest common denominator) and certain functions being disabled if memory sizes are mixed. The reason for this is that memory interleaving is a sort of 'computer math trick' that allows the RAM to have faster throughput if all of the memory address' align (which means the sticks would have to be at least the same sizes). Your motherboard/chipset combination will determine what your limits are based on the memory types you put in, in other words, memory functionality (dual-channel/interleaving) is a function of the motherboard/chipset you use and not necessarily of the RAM itself. If you have 2 sticks of 4GB (2x4GB) in slots 1 and 3 (usually how it goes in dual channel) they should be of the same type (speed/latency/etc.) otherwise the RAM won't 'work' at all (won't be recognized) or the RAM will 'run' at the lowest speed of the two. Mixing the sizes in the banks (2x2GB and 2x4GB) should keep the 'dual-channel' configuration if that's an option in your chipset and the dual sticks are the same (i.e. speed), but it could depend if you will still have memory interleaving as that is an algorithm employed by the chipset manufacturer which uses 'banks of memory' (could be the entire stick or a few chunks of it).
In the long run this might not affect you depending on what you do. If you're only ever doing basic (not video/games) web surfing, and document editing, even some power stuff may not take a hit from this. If, however, you're a gamer, like watching a lot of videos, do any sort of virtualization, are an enthusiast, etc. etc. memory interleaving 'could' make a significant difference to you. I say 'could' because with any build there are a lot of factors that determine your performance but RAM and HDD are usually the first things to get upgraded.
You can use a tool called CPUz to check out what your computer is reporting 'up-the-chain' if you will (i.e. from the BIOS to the OS) about your hardware configuration (including your RAM).
Hope that helps