Optimally position 2 pairs of RAM

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pizzaboyuk

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Apr 9, 2017
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I have 2 pairs of DDR3 memory which I'd like to optimally position on the motherboard.

The newest pair are DDR3 8GB running at 2400MHz. The old pair are DDR3 2GB running at 1600MHz.

I currently have the 2GB in slots A1 and B1. With the 8GB in A2 and B2. Am I supposed to have the pairs together in a channel or according to the colour of the slots?

Ideally, of course I'd love the idea of having 20GB of RAM to play with, but will the motherboard automatically optimize the speed of the memory to use? My motherboard is an ASUS Z97-P.

Can anyone also advise on how I can check the speed of the RAM? CAM and CPU-Z don't appear to offer any help.

Cheers
 
Solution
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So @unclebun is **sort of** right.

There's no guarantee that all the RAM will work together. In my experience you'd be extremely unlucky if it didn't work at all, but there's not guarantees when you mix-and-match RAM sets. The other issue is that you can only run with one set of timings, meaning all the RAM will run at 1600mhz, not faster. Theoretically you could try overclocking, but that's unlikely to be worth the hassle with 4 unmatched DIMMs.

So TLDR 20GB... yes probably, but only at 1600mhz.

To be honest, I'd prefer 16GB @ 2400Mhz than 20GB @ 1600mhz. That extra 4GB is very unlikely to make a big difference. 16GB is plenty for most uses. With a new 16GB matching kit it will work for sure, and you can just turn on the XMP...
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unclebun

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The memory slots are positioned in pairs on the motherboard. Closest to the cpu are A1 and A2, a space, and then B1 and B2. For dual channel operation you put a matching pair in A1 and A2, and a matching pair in B1 and B2.

As to the differing memory speeds, the manual has this warning: "Always install DIMMs with the same CAS latency. For optimal compatibility, we recommend that you install memory modules of the same version or date code (D/C) from the same vendor. Check with the retailer to get the correct memory modules. "

In the old days, what would happen when you had memory of different speeds installed was the memory would all be run at the speed of the slowest module. You may still be able to do that. But with the faster speed memory and the newer motherboards, there are a lot more memory incompatibility issues, so it might not work. You can try it with all the modules, and may be able to have 20GB running at 1600. But if it doesn't work, just run the 16GB at 2400.
 
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thx1138v2

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Jun 18, 2011
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You have the modules installed incorrectly. Section 1.4 of the manual covers the system DRAM configuration. From the manual:
Channel A DIMM_A1 and DIMM_A2
Channel B DIMM_B1 and DIMM_B2

The ASUS Z97-P supports Intel Flex channels so it's OK to use different capacity modules as long as the modules in a single channel (A or B) are the same.

But since the modules have different speeds they will all run at the lower speed when they are all installed. To get the higher speed you must use only the two higher speed modules.

You can download the ASUS Z97-P here.

I suspect that once you have the modules installed correctly, CPU-Z will display the speeds correctly. Right now you have different speed modules in the same channel.
 
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rhysiam

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Mar 24, 2013
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So @unclebun is **sort of** right.

There's no guarantee that all the RAM will work together. In my experience you'd be extremely unlucky if it didn't work at all, but there's not guarantees when you mix-and-match RAM sets. The other issue is that you can only run with one set of timings, meaning all the RAM will run at 1600mhz, not faster. Theoretically you could try overclocking, but that's unlikely to be worth the hassle with 4 unmatched DIMMs.

So TLDR 20GB... yes probably, but only at 1600mhz.

To be honest, I'd prefer 16GB @ 2400Mhz than 20GB @ 1600mhz. That extra 4GB is very unlikely to make a big difference. 16GB is plenty for most uses. With a new 16GB matching kit it will work for sure, and you can just turn on the XMP profile in the BIOS and you should then boot at 2400Mhz... job done.


With respect, that's incorrect. Channel A services A1 & A2, Channel B services B1 & B2. For dual channel you want one stick of RAM in each channel, so A1+B1, or A2+B2 for your matching sets.
OP, if you really want your 20GB @ 1600mhz, then A1 and B1 for your 8GB sticks, with A2 and B2 populated with the 2GB.

The memory tab under CPU-Z should report your DRAM channel mode and frequency.
- "Channel #" will tell you dual or single channel mode
- "DRAM frequency" will tell you the base RAM frequency. Because it's "DDR" RAM (stands for "double data rate") you double what CPU-Z displays to get your RAM frequency. So you'd expect CPU-Z to report 800mhz with all slots populated, and 1200Mhz if you go with just your 16GB kit and enable the XMP profile.

The BIOS should also report RAM timings and dual/single channel operation.
 
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pizzaboyuk

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Apr 9, 2017
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Cheers guys.

Having a re-think about this.

To be honest, I can't recall my system running upto 8GB of RAM, so might as well just remove the slower RAM to be on the safe side.
 
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