RAM. Is dual channel really that important?

[Mr.Clark]

So I bought a cheapy Skylake motherboard and CPU. Re-used my current RAM and GPU.

I had 4x4GB RAM, which was the max that my old Shuttle could take. I've run a memtest on it and found one stick was fucked. So currently on 12GB.

Is it more important that I get a matched pair (so get 2x 8GB sticks and bag off a working 4GB one) or since I'm not going for bleeding-edge every-fps-is-precious, can I just put a single 8GB in the empty slot and end up with 20GB?

[RB]

Just get another 4GB. Matched pairs don't have to be siblings just the same size and speed.

[kingweed]

aye, ram can only run at the speed of the slowest one you have

[Tinlad]

I found this article helpful, when I has a similar question: Memory Scaling on Haswell. I know it's talking about Haswell, and not Skylake, but the conclusions are likely to still hold true.

TLDR;

[The] importance of order is such that:

1. Amount of memory
2. Number of sticks of memory
3. Placement of those sticks in the motherboard
4. The MHz of the memory
5. If XMP/AMP is enabled
6. The subtimings of the memory

But it probably depends on your workload - if you need over 16GB RAM then obviously 20GB of slower RAM will be better than 16GB of faster RAM. But if that's not the case, then the opposite's true.

Assuming you're not frequently using over 16GB RAM I'd just get another 4GB stick.

[Mr.Clark]

But... bigger numbers!

No, you're right. I don't know if I've ever managed to use all 16GB. And I don't game that much, although it's been bliss today to have SWTOR on for literally hours and not have the infernal machine blue screen on me multiple times.

Also, a 4GB stick seems to be less than £20 on Crucial, so there's that.