I would keep all of the RAM the same speed. As Kelly said, if it's faster it will be fine but you may need to tweak the BIOS to get it to work reliably.

Speaking of "reliably"... if you do plan to buy all new memory, I would ONLY buy memory that is on the approved memory list for your motherboard manufacturer. Every manufacturer tests memory with their motherboards and certifies it. Buying memory that is not on that list is taking a chance that it might not work or might not work reliably. When I use to build my own PC I would only buy approved memory and I always had a reliable system.

~jr

Thanks, I'm trying to do a gradual upgrade to my pc, since I'm not floating in cash right now. I just got a sapphire radeon r9 290x video card from the bay for $225. And now I'm starting to save for a new motherboard, CPU and DDR4 ram. So I guess for now I will just get the cheaper 1866 ram second hand off eBay.

In my experience I found reliability issues with no-name memory sticks. When I stuck with major brand memory, no worries.

And it's very useful to run something like "Memtest" which exercises the ram five ways from Sunday in a continuous loop. If it can run Memtest for 24 hours, you're good to go.

A utility app like Speccy can give you some good info your system and memory. Info like details on motherboard maker, chipset, and memory profiles used and available.

DIY motherboards often times advertise super high clock speeds, but I find sticking with the core Intel rating for the chipset to be the most stable. Stability is most peoples biggest complaint, and I think most of the time people do not realize that they are shooting themselves in the foot with super cranked up settings from some "how to over clock" article they read. If you can find a stable overclock speeds above the Intel chipset standard, fantastic, you got some chips with few manufacturing flaws.

Motherboards have different memory controller configurations. X58 has 3 channels, x99 has 4 channels. Most Gen1-i7 thru Gen4-i7 have dual channel controllers. Populating ram in the correct slots can make a difference. Some boards will drop dual channel mode with more than 1 stick per channel, and so high density single sticks in each channel can help. The difference between maintaining dual channel mode vs single is only like a 20-30% speed increase. This speed increase is probably hard to quantify since modern windows releases like the most ram you can throw at it. I would take 16GB or 32GB of single channel vs, 8GB of dual channel. This is because of the amount of caching that Windows does, and executing from cache memory will always be much faster than even SSD disk calls.

"Winsat mem" from an admin command prompt will tell you what your memory bandwidth is. Doing before and after, to make sure you are not losing bandwidth on your new configuration.

Kelly's correct. Just double check with your MB manual that putting RAM in all 4 channels won't slow anything down (most MB just want RAM of the same set in certain slots so it could be slots 1/2 & 3/4 or 1/3 & 2/4).

That list the manufacture has for compatible RAM is just ones tested. I've never had the RAM listed be more/less reliable then ones not on that list. RAM on that list can still not work very well or be junky compared to other sticks.

Think of it like connecting speakers to an amp. If your amp can deliver 300 Watts then you want speakers that can handle 300 Watts. It's certainly ok to use 400 Watt speakers, but the amp will still only deliver 300 Watts. You don't want to connect 150 Watt speakers as the amp will still try to deliver full power and could damage them.

With memory speed, you just want chips that can handle at least the speed the mother board uses. The chips won't try to force the motherboard to run faster; they're passive and are simply accessed at the motherboard's speed. So it's perfectly fine to use faster memory. The memory chip speed is simply a measure of how fast they *CAN* be accessed, not how fast they run.

Often half the slots will be one color, while the other half are another color. I've often seen that two of the RAM slots are blue while the other two are dark grey. Put matching sticks in the same color. So, your two fast sticks would be paired in one color while the two new sticks in the other color. Well, if your slots are color coded, that is. If not, just do a google search for the model of your motherboard and look for the memory diagram. That will tell you which slots are paired with which. Most modern motherboards use memory in pairs in order to speed up access, similar to RAID 0 for hard drives. If the pair doesn't match there can be timing errors that can slow down the access, or even cause reads to fail. It's also possible the motherboard may decide the chips can't be used as a pair and will use them separately, effectively halving the speed of memory access.