Question Mixing DD4 Frequencies in Quad Chanel with 8 sticks.

rubenhak

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Hi,

I've got Intel® Core™ i7-6950X on Asus X99-DELUXE board.
Currently using:
Corsair Vengeance LPX 32GB (4 x 8GB) DDR4 2133MHz C13 (CMK32GX4M4A2133C13)

I'm thinking to get:
Corsair Vengeance LPX 64GB (4 x 16GB) DDR4 2400MHz C14 (CMK64GX4M4A2400C14)

The question is what would happen if I populate all 8 sticks? Will I get all 96GB ram? What would be the speed - 2133 or 2400? Will the quad-channel work?

Thanks,
Ruben
 

Karadjgne

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Yes, ram adds. So 96Gb.

Ram always defaults to the slowest speed, highest voltage, worst timings. So you'd have 96Gb running at 2133MHz unless you could first get that 2133MHz ram OC'd to 2400MHz manually, then add the new 2400MHz ram, giving you 2400MHz speeds.

Quad channel only requires 4x sticks, one in each of A, B, C and D pairs. Adding the second batch of 4 just adds a second quad channel setup, which is still quad channel.

You just need to be careful where you put the pairs as that board is fully capable of single, dual, tri, quad or flex modes.

What'll happen is flex mode. When you mix sizes, you'll get an equal amount used, the leftover used last.
16Gb = 8+8. So the 4x8 and first 8 of the 4x16 will pair off, 4x8 x2. The remaining 32Gb will still be in quad channel, but gets used only after the first 8x8 (64Gb) is saturated.

That's assuming the 2 kits actually work together, getting 8 stable ram sticks is the hardest thing to do with any kit, has multiple more chances of failure than mixing just 2x single sticks.
 
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rubenhak

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So I will get two quad-channels running in parallel? What do you mean by "assuming 2 kits work together"? Are there chances that they wouldn't work at all?

Would the identical two kits (the 64GB 2400MHz) work together?
 

Karadjgne

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A kit is 1 or more sticks that have been tested by the factory as being compatible, with each other. You get a 4x kit, all 4 sticks were tested simultaneously, with each other, any stick not compliant being replaced until all 4 were good.

A stick is a pcb with several chiplets of silicon welded to it. Those chiplets all come from the same sheet of silicon, so are naturally compatible. This is why you'll often see serial numbers on ram on a kit being consecutive, or close to it.

Brand, color, heatsink, means nothing. There's no guarantee that even identical looking ram, from the same store, same shelf, same day, one after the other, will be compatible. Different silicon chiplets from a different sheet of silicon.

You could mix 2x SkHynix Corsair LPX with 2x Micron Crucial sticks and have the exact same chances of compatibility as 2x identical kits of 2x sticks.

Your results will be 1 of 3 options. The kits will be compatible as is. The kits will be compatible after some tinkering with voltages or speeds or timings or any combination of those. The kits just simply don't like each other, at all and refuse any kind of working relationship.

This is why it's strongly recommended you purchase the entire amount wanted, in the speeds and model wanted, as a single kit. It's the only guarantee of compatibility out of the box.

Otherwise there's a decent likelihood of necessary tinkering or complete failure, and it's compounded exponentially with every stick. It's very, very hard to get all 8 sticks in compatibility, especially at higher than default speeds. It only takes 1 stick to be a little off and not like one other stick and the whole thing is bunk, it takes forever to find which stick is off. If at all.

And you can't return just 1 stick, you must return all 4x, and the process repeats. Maybe the new 4x will be compatible, maybe not. Could be the 1x off stick is on your original 4x, good enough for those 4x, but 100 kits later and still no joy.
 
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Karadjgne

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It's possible. It can happen, often does, but just as often doesn't. There's absolutely no guarantee either way. It's totally pot-luck.

It's very likely that at least once a month, someone, somewhere will win the state lottery, but whether that person is you, who knows.
 
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rubenhak

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Thanks folks, what a catch! 64GB max, meaning problem even doesn't exist :)

"8 x DIMM, max. 64 GB, DDR4 2800 (O.C.)* / 2666 (O.C.)* / 2400 (O.C.)* / 2133 MHz, non-ECC, un-buffered memory"

Do I have to over-clock / increase voltage for 2400 memory to work, or just picking XMP profile is enough?
 

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