Mix memory: 1600 and 1333

ldm_forever

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Oct 31, 2017
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I have a b85m-e/br motherboard running with 2 x 2gb ddr3 1600 mhz.

Whats is the best option?

A) use 2x4 gb 1333 mhz in dual channel
B) try to use 2x4 gb 1333 AND 2x2 gb 1666 (will this work in dual channel)
C) keep with my 4 gb 1600 mhz in dual channel
 
Solution
There's no telling when it comes to mixing RAM. Even with same specs from same manufacturer.

Least likely way to have no compatibility/stability issues is to buy RAM in packs that are (tested and) rated to run with each other in dual channel or any other configuration supported by the chipset and CPU.

Option C is fasteras it runs at higher clock/speed. You'd have less capacity than option A but it's faster. If you use and OS or applications that require more RAM then go with option A.

Again back to mixing RAM in option B. I might work but at the clock speed of the slowest RAM which is 1333 here. You can only know for sure if you test/boot the system with them.

I would choose 8GB at 1333. Two 4GB sticks.
There's no telling when it comes to mixing RAM. Even with same specs from same manufacturer.

Least likely way to have no compatibility/stability issues is to buy RAM in packs that are (tested and) rated to run with each other in dual channel or any other configuration supported by the chipset and CPU.

Option C is fasteras it runs at higher clock/speed. You'd have less capacity than option A but it's faster. If you use and OS or applications that require more RAM then go with option A.

Again back to mixing RAM in option B. I might work but at the clock speed of the slowest RAM which is 1333 here. You can only know for sure if you test/boot the system with them.

I would choose 8GB at 1333. Two 4GB sticks.
 
Solution
Usually, ram will match lower specs ram and work.

While it might post, if voltage and timing a really different you will run into slowdowns, BSOD or random errors.
If it's the case you will have to tweak and it's a trial an error situation.
Bottom line it could just not work.
 
If all RAM modules have a common set of timings and bus speed that they can run at, you can usually mix them. Of course, nobody will guarantee it to work, but at the same time, nobody can guarantee that it won't, either.

The best advice has already been given which is to buy a single kit that meets your needs. It's easy to understand that's not always a practical route, especially with high RAM prices.

Beyond that, it's going to depend on your particular situation, whether higher bandwidth or greater capacity is going to best suit your usage.

Personally, I usually lean more toward capacity than speed, as when a system runs low on RAM capacity, it tends to be far slower than even the slowest RAM modules available.

Since you have the capacity to run 4 RAM modules, if the opportunity is available to you to attempt the mixed configuration, I don't see any harm in trying it, but I certainly wouldn't purchase new modules just to try them.

You will probably see best results from keeping the 1333 MHz modules and the 1600 MHz modules on separate memory controller channels. I'm going to speculate that means one 1333 MHz module in a yellow slot and one in a black slot, but I'm not sure which ones. The same would apply for the 1600 MHz modules. The manual may point out which memory slots correspond to which memory controller.