Mixed RAM pairs and dual channel slots.

[FifthTangent]

If one was to have two different pairs of RAM, in what order does one install them to function properly in dual channel with its matching module?
[slots 1 - 3 and 2 - 4] or [slots 1-2 and 3 - 4] ?
 

[Fasauceome]

alternating slots. Most boards have color coded slots, so you'd place pairs in the corresponding colors.

[FifthTangent]

For the sake of argument the ram clocks are the same, and the MOBO is a Asus Prime Z390 - A.
The RAM pairs are not matching model numbers though.

[FifthTangent]

Just now, Fasauceome said:

alternating slots. Most boards have color coded slots, so you'd place pairs in the corresponding colors.

That's my understanding, but I've had my senior tech tell me that when it's a mixed pair that they NEED to be installed [1-2, 3-4]
and that the alternated slotting is only for installing a single pair of dual channel.
I've been unable to find any official documentation to support that claim.

[Hans Christian | Teri]

3 minutes ago, FifthTangent said:

That's my understanding, but I've had my senior tech tell me that when it's a mixed pair that they NEED to be installed [1-2, 3-4]
and that the alternated slotting is only for installing a single pair of dual channel.
I've been unable to find any official documentation to support that claim.

Nor will you be able to, that claim is false.

[Hairless Monkey Boy]

6 minutes ago, FifthTangent said:

That's my understanding, but I've had my senior tech tell me that when it's a mixed pair that they NEED to be installed [1-2, 3-4]

I agree with this person. Configuring them this way will allow the motherboard to assign different timings to the different channels, which can improve compatibility.

 

But if it works with [slots 1 - 3 and 2 - 4] then you can leave it that way.

[BlueChinchillaEatingDorito]

4 minutes ago, FifthTangent said:

That's my understanding, but I've had my senior tech tell me that when it's a mixed pair that they NEED to be installed [1-2, 3-4]
and that the alternated slotting is only for installing a single pair of dual channel.
I've been unable to find any official documentation to support that claim.

The motherboard manual overrules claims from any "senior tech".

[FifthTangent]

1 minute ago, BlueChinchillaEatingDorito said:

The motherboard manual overrules claims from any "senior tech".

I looked through the manual for the MOBO in question. It states 1 stick, 2 stick, and 4 stick configurations... but nothing specifically about non-identical pairs.
I just took the intuitive leap that if 2-4 are automatically Dual channel pairs, that the other channels (1-3) would be the other channeled pair. 

[FifthTangent]

8 minutes ago, HairlessMonkeyBoy said:

I agree with this person. Configuring them this way will allow the motherboard to assign different timings to the different channels, which can improve compatibility.

Will that run all of them in single channel mode with configured / different timings? or will it also be able to dual channel within 1-2 and 3-4?.

[Fasauceome]

4 minutes ago, FifthTangent said:

I just took the intuitive leap that if 2-4 are automatically Dual channel pairs, that the other channels (1-3) would be the other channeled pair. 

you indeed will often see an improved situation with the paired dimms in each channel.

 

sometimes you might run into a compatibility or stability problem, miraculously solved by the dimm pairs being in mixed channels, but it's far from the ideal configuration.

[BlueChinchillaEatingDorito]

3 minutes ago, FifthTangent said:

I looked through the manual for the MOBO in question. It states 1 stick, 2 stick, and 4 stick configurations... but nothing specifically about non-identical pairs.
I just took the intuitive leap that if 2-4 are automatically Dual channel pairs, that the other channels (1-3) would be the other channeled pair. 

I'm not 100% sure if it works that way. I'll have to double check. I believe they will be forced to run in single channel at the lowest speed of the 4 sticks. 

 

[Helpful Tech Witch]

9 minutes ago, HairlessMonkeyBoy said:

I agree with this person. Configuring them this way will allow the motherboard to assign different timings to the different channels, which can improve compatibility.

 

But if it works with [slots 1 - 3 and 2 - 4] then you can leave it that way.

if it doesnt work. But it doesnt need to, it should be if its not working in dual. 

[Hairless Monkey Boy]

1 minute ago, FifthTangent said:

Will that run all of them in single channel mode with configured / different timings? or will it also be able to dual channel within 1-2 and 3-4?.

Unless they are different capacities, they will all be dual channel. If they are different capacities, then they will run mixed or single channel depending on the motherboard.

[FifthTangent]

1 minute ago, HairlessMonkeyBoy said:

Unless they are different capacities, they will all be dual channel. If they are different capacities, then they will run mixed or single channel depending on the motherboard.

Assuming same capacities wouldn't this just be making it dual channel with on stick from each pair in [1-2,3-4] mode?
Is that more stable because then both sets are technically symmetrical now? 

[Hairless Monkey Boy]

1 hour ago, FifthTangent said:

Assuming same capacities wouldn't this just be making it dual channel with on stick from each pair in [1-2,3-4] mode?
Is that more stable because then both sets are technically symmetrical now? 

I think you have it opposite. 1 and 2 are channel A. 3 and 4 are channel B. Ordinarily, with a 2 stick set, you put one stick in channel A, and the other in Channel B.  When you have two different sets and you put one pair in 1-2 and the other pair in 3-4, then each channel contains only one type of RAM, with one set of timings. This ensures compatibility. In your case, since the two kits are equal capacity, this will probably be the best way to do it.

 

I'll detail some of my experience with this, but this is a specific example and some of this may not apply to your setup.

 

A while back, I was running an Asus Z97A with 16GB (4x4GB) of DDR3 2133 9-11-10-28 1.65V. I wanted to upgrade my memory capacity, and decided that 24GB would be enough, so I bought a kit of 8GBx2 (16GB) to replace two of the 4GB sticks. I chose RAM with the most similar specs I could find, which turned out to be 2133 10-12-12-31 1.6V. I explored all of the options for installing the RAM.

 

Key:

BLUE: 8GB Module

GREEN: 4GB Module

 

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In this configuration, my motherboard was reading the XMP settings from the lower latency 4GB modules and applying those settings to all of my RAM. It was not stable since the 8GB modules could not operate at 9-11-10-28.

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In this configuration, my motherboard operated the different channels with different timings. The 8GB modules in channel A were at 10-12-12-31 and the 4GB modules in channel B were at 9-11-10-28. It was stable, but I had only 16GB of dual channel memory with another 8GB of single channel memory.

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|| ||

 

In this configuration, my motherboard was reading the XMP settings from the higher latency 8GB modules and applying those settings to all of my RAM. It worked great. I had 24GB of dual channel memory with 12GB per channel, and the timings were set to 10-12-12-31 which worked for both kits. I OCed this setup to 2200MHz with 9-12-11-28 1.7V and it worked flawlessly like that for a couple years.

 

[FifthTangent]

6 minutes ago, HairlessMonkeyBoy said:

I think you have it opposite. 1 and 2 are channel A. 3 and 4 are channel B. Ordinarily, with a 2 stick set, you put one stick in channel A, and the other in Channel B.  When you have two different sets and you put one pair in 1-2 and the other pair in 3-4, then each channel contains only one type of RAM, with one set of timings. This ensures compatibility. In your case, since the two kits are equal capacity, this will probably be the best way to do it.

 

Ok... so running it in 1-2, 3-4 allows each channel to have its own configuration, and therefore being more stable... But this means it's not running in dual channel mode?
So this becomes more ideal in asynchronous ram configurations if timings are making it unstable...
But in your examples your most functional config was to split the RAM half and half between the channels. Yes?

[Hairless Monkey Boy]

7 minutes ago, FifthTangent said:

But this means it's not running in dual channel mode?

Only if the RAM has different capacities. In that case it will run either single channel or mixed. If mixed, Windows will fill dual channel memory first. If all the RAM has the same capacity, it will run in dual channel mode.

7 minutes ago, FifthTangent said:

But in your examples your most functional config was to split the RAM half and half between the channels. Yes?

Yup! Because my RAM had similar enough timings that I could get it to work. If this works, then go ahead and leave it this way.