Is it OK to use 1 x 8GB RAM stick in a Dual Channel (4 slots) ?

pmap93 · Jul 6, 2014

Hello!

I'm planning my next build

I'm wondering if it is safe to use ONE 8GB stick of RAM to achieve 8GB in a Dual Channel slot?

Or it is completely necessary to use a pair like 2 x 4GB ? :eh?:

Thanks in advance

Mr.Scott · Jul 6, 2014

One stick will not give you dual channel. It works in pairs.
A single 8 gig stick in any slot will give you 8 gig in single channel.

caddi daddi · Jul 6, 2014

it will work, but in single channel mode, you will get less out of it than you would with 2x4 gig sticks.

ATMINSIDE · Jul 6, 2014

Its safe, the computer will run, but it will have half the bandwidth of a 2x4GB setup.

You WILL notice the difference.

pmap93 · Jul 6, 2014

Thank you very much for your lightning fast replies

GearingMass · Jul 16, 2014

Crap I was about to make the same mistake in my new build. Looks like I'll be running by micro center today. :-/

Silver_Pharaoh · Jul 16, 2014

Question: Would it be better to run 4x2Gb sticks instead of 2x4Gb?

Quad-channel? :shrug:

(Sorry for jacking)

GearingMass · Jul 16, 2014

From my very new understanding, 4x2GB would only be better if your motherboard supported quad channel. If it's only duel channel, I would think it better to stick with 2x4GB and leave the other two slots open for potential future expansion.

ATMINSIDE · Jul 16, 2014

Silver_Pharaoh said:
Question: Would it be better to run 4x2Gb sticks instead of 2x4Gb?

Quad-channel?
(Sorry for jacking)

You must be on LGA 2011 for quad channel.

Silver_Pharaoh · Jul 16, 2014

Thanks.

Meh, didn't think I could run quad anyway, just curious

Woomack · Jul 17, 2014

Most new popular IC perform like:
single 4GB < 8GB
dual 2x4 or 4x4GB < 2x8 or 4x8GB
quad 4x4 or 8x4GB < 4x8 or 8x8GB

Older 4GB modules were double sided and 4GB = 8GB in general performance but you won't find them in any new kits.

Also 3 modules are usually working as dual channel and have the same performance as 2 or 4 modules on a dual channel platforms.

EarthDog · Jul 17, 2014

Also 3 modules are usually working as dual channel and have the same performance as 2 or 4 modules on a dual channel platforms.

Doesn't the 3rd stick run in single channel?

Woomack · Jul 17, 2014

At least on Z77, Z87, Z97 and A88X I was running 3 sticks in dual channel without performance drops. The same 4 sticks on X58 were working as triple channel when placed in correct slots.

ATMINSIDE · Jul 17, 2014

Woomack said:
At least on Z77, Z87, Z97 and A88X I was running 3 sticks in dual channel without performance drops. The same 4 sticks on X58 were working as triple channel when placed in correct slots.

I believe EarthDog is correct here.
The OS will fill the dual channel capacity first, then fill the single channel.

So, if you had 2x4GB and 1x8GB you would have to use >8GB to see a performance drop.

Woomack · Jul 17, 2014

ATMINSIDE said:
I believe EarthDog is correct here.
The OS will fill the dual channel capacity first, then fill the single channel.

How can it fill dual channel and then single channel when there is one dual channel and all RAM is shared, not split ?

So, if you had 2x4GB and 1x8GB you would have to use >8GB to see a performance drop.

I'm not sure what are you talking about here.

EarthDog · Jul 17, 2014

Woomack said:
At least on Z77, Z87, Z97 and A88X I was running 3 sticks in dual channel without performance drops. The same 4 sticks on X58 were working as triple channel when placed in correct slots.

X58 is a bit different in that it could do that (had more flexibility on channeling). I wasn't sure the 'mainstream' platform could allocate 3 sticks in a dual channel configuration. I was thinking it would run the dual ch sticks as dual and the single as single...

Let me look up a couple of manuals and see what they say. I recall seeing one that showed with three, 2 were in dual channel while the 3rd was in single...(though I could be off - hang tight)........

I'm not sure what are you talking about here.

He is saying that the 2x4GB is dual, while the 1x8GB is single. It will use the 2x4GB dual capacity first, but after that 8GB it will be single channel...

Im thinking of it this way... if dual channel requires two slots to be populated, how can 3 also be dual as it does not have the 2nd stick to run dual channel?

Woomack · Jul 17, 2014

Last time when I was using 3 sticks in dual channel was last week. My daily PC is now based on ASRock A88X Extreme6 and I was using 3x 4GB Avexir/Elpida based single sided modules. Every soft saw dual channel and performance was the same as on 2 modules. I sold all these memory sticks last friday.

Most manuals are saying that 3 sticks = single channel, 2 or 4 are dual channel but in real it works also with 3 just sometimes depends from a board or BIOS.

EarthDog · Jul 17, 2014

Most manuals are saying that 3 sticks = single channel, 2 or 4 are dual channel but in real it works also with 3 just sometimes depends from a board or BIOS

That is what I am saying, we really do not have software that shows what dual/single channel for each DIMM. I believe the 2x whatever is dual channel but the single stick is single in a 3 stick setup. Performance would be the same unless you got past the dual channel capacity (as ATM said) is what I also think happens.

Is there any way to conclusively find out via software for each DIMM?

I suppose I can reach out to MSI and see what they say about it.

Woomack · Jul 17, 2014

I think it's not about modules but about memory controller. If it fills enough banks to work at higher bus bandwidth then it's activating dual channel. Support for that has to be made in BIOS and I think that manufacturers are protecting themselves from incompatibility issues saying that 3 modules will work only in single channel. The same was on earlier boards regardless of used chipset.
Soft is now showing info about single modules but about whole memory controller bandwidth as all RAM is shared.
Nforce2 was working in dual channel on 3 modules and these boards had 3 slots. All newer chipsets are officially supporting 2/4 or more modules in dual channel. Manufacturers are not even testing compatibility with 3 modules ( except X58/server boards ).

EarthDog · Jul 17, 2014

I also agree it is how the memory controller deals with the number of sticks, no doubt. I still think with 3 sticks 2 are dual, the third is single though as the third stick does not have a 'partner' for dual channel.

According to the ASUS manual for z87 Sabertooth, when running mismatched capacity DIMMs, it will allocate the lowest common denominator (say its a 4GB stick and 8GB stick) in dual channel (so 8GB total) and the remaining 4GB in single channel. That tells me the controller has the flexibility to run single and dual channel at the same time. I am aware we are not talking mismatched capacity, but wanted to share that as an example of the flexibility of the IMC to run both dual and single at once. I believe intel calls this "Flex mode".

ASUS Z87 Sabertooth manual - See page 1-12, first paragraph

EDIT: Here we go...http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm#flex

Rules to enable dual-channel mode

To achieve dual-channel mode, the following conditions must be met:

Same memory size. Examples: 1 GB, 2 GB, 4 GB.
Matched DIMM configuration in each channel
Matched in symmetrical memory slots

Is it OK to use 1 x 8GB RAM stick in a Dual Channel (4 slots) ?

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