Question about mixing RAM kits

[yoadknux]

Hi,

This is a very general question. I know that for example if I have a 1x4 stick and another 1x4 stick and I try to make them run together at a dual channel configuration, there is a good chance they will not play well together. However, let's say that I have a 2x4 dual channel kit and a different 2x4 dual channel kit, and I place them in the right slots on the motherboard, and lets put timings and frequency out of the equation (say they have some common stable timings). Does kit 1 actually interact with kit 2?

In other words, if I have 2 RAM kits (2x4 sticks A, 2x4 sticks B), and I place sticks A at dual channel "1" and sticks B at dual channel "2", will they always work together?

Also asking about 3x4 + 3x4 (matching triple-channel kits) and 4x4 + 4x4 (matching quad-channel kits).

Thanks!

 

[EarthDog]

Mixing and matching isnt typically a good idea.

Same capacity same speed and primary timings is your best bet for compatibility though, yes. All four will work in dual channel (six in tri and 8 in quad), yes.

 

[Alaric]

As long as you're not on the ragged edge of your CPU/mobo's capabilities it's generally not been an issue for me. If the RAM is different speeds/timings it will default to the slower RAM's default numbers. Sometimes you can play within that envelope, sometimes not.

 

[Vishera]

I just ordered an additional 8GB of RAM. Also Crucial, also from the Tactical line, same color and design for the heatspreader, everything. The only difference I can see is there's a sticker on my first kit saying XMP should be able to run at 3000MHz with 15-16-16-32 timings, and the new kit says 2666. I haven't noticed any issues, and in fact, since adding the second kit, I've been able to get the first kit to run stable at a higher speed (before, I couldn't get it to boot reliably any higher than 2666, but I'm running smooth at 2800 since adding the second kit). Though, I would personally chalk this up to mere coincidence.

So, in my personal experience, there isn't too much of an issue if you're using four sticks, two from one kit, two from another. The kits run in dual channel each, anyways, so it's not like you're missing out on quad channel or anything. From what I can tell, they're separate.

 

[OC-NightHawk]

Mixing and matching isnt typically a good idea.

Same capacity same speed and primary timings is your best bet for compatibility though, yes. All four will work in dual channel (six in tri and 8 in quad), yes.

Op, One thing to keep in mind if mixing RAM only expect the performance of the lowest common denominator. Even RAM with the same specs if not sold together in one package can be different which is what EarthDog is saying.

I'm far from a expert but it's my understanding that it's sort of similar to overclocking SLI graphics cards where even if one card (pair for memory) can do better because the other card (pair) can't it can't either. So that effectively lowers your chances to get high speed on the RAM as a whole.

That said my Core i7 5930K system has two dual channel kits (the same make and model purchased at the same time) as opposed to a Quad channel kit because at the time the prices where outrageous. It's only DDR4-2400MHz and I haven't tried overclocking the RAM but they have no issues at their advertised speeds.

 

[Woomack]

I often get for tests single sticks, not a full dual/quad kit but PN is the same and used IC too.
With RAM it's more like motherboard will read SPD/XMP from first modules, if it's good enough for all other modules then it will work, if not then mobo won't see other sticks or won't boot at all.
Standard SPD settings should be the same for all memory kits, XMP settings are different. Usually when you mix DDR3/DDR4 then all works fine at low clocks. Problems are starting at higher clock, usually marked as XMP profile, or above that.

Crucial is usually a safe option when you add memory modules after some time after purchase. Crucial uses the same product number for memory with the same profile and memory IC (if not the same then similar like the same IC density and type). So when you buy dual channel kit under some PN then after couple of months you will find memory kit under exactly the same PN with exactly the same specs. Problem can be if you won't find the same PN as different PN can be on a different IC, dual/single rank, with different timings etc.
There are kits where one letter is different in PN but it means that one kit is based on DDR4-2400 and the other one on DDR4-2666 IC ... in both cases with DDR4-2666 XMP profile.
Many other manufacturers are replacing IC or memory profiles within the same PN.

@Vishera
3000 CL15 and all higher Crucial kits are based on Samsung IC. Everything below is on Micron IC. New 3000+ CL17 kits (Sport AT) are on Micron IC.