Question Memory Does number of sticks effect speed?

Oct 22, 2022
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Hello,

My motherboard states the following:

MEMORY4x DDR5, Maximum Memory Capacity 128GB
Memory Support DDR5 6666+(OC)/6600(OC)/6400(OC)/6200(OC)/6000(OC)/5800(OC)/5600(OC)/5400(OC)/5200(OC)/5000(OC)/4800(JEDEC) MHz
Max. overclocking frequency:
• 1DPC 1R Max speed up to 6666+ MHz
• 1DPC 2R Max speed up to 6000+ MHz
• 2DPC 1R Max speed up to 6400+ MHz
• 2DPC 2R Max speed up to 4000+ MHz

Supports Dual-Channel mode
Supports non-ECC, un-buffered memory
Supports AMD EXPO
Does 1DPC 1R Max Speed up to 6666+ MHz mean I can put 2, 32GB sticks and get that speed?
Does 2DPC 1R Max Speed up to 6400+ MHz mean I can put 4, 32 GB sticks and get that speed?

Or am I completely off?

Thanks
 

Math Geek

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dpc means dimms per channel. 1R and 2R means either single or dual rank of the individual stick. channel is of course the 2 slots that make up a single channel. usually like slot 1 and 3 or 2 and 4. mobo manual will tell you which pair together and which to use if only one channel is populated

so from top to bottom is

single stick single rank
single stick dual rank
2 sticks single rank
2 sticks dual rank

you get the rank info from the specs of the ram stick. and of course the + at the end of the speed means you could possibly oc the ram but no guarantee it will work.

and just fyi, 32 gb sticks will almost always be dual rank ram. or at least i don't recall seeing any single rank 32gb sticks though i admit i don't look real hard for them.
 

Karadjgne

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Almost all sticks 16Gb and larger are dual rank, size limitations of the chips mean its a must, physically.

Ram speeds are dependent on 1 thing, the speed of the ram as set by XMP or OC values.

That table represents current memory controller capability. So if using a single stick per channel, and that stick is single rank ram, you can use upto 6666+ ram. If the ram is dual rank, anything above 6000+ is pot luck whether it'll work with XMP settings but should work if manually set to 6000.

DDR5 memory controllers don't like 4x sticks. Especially dual rank. The way it works is dual rank is 2x single ranks in parallel, but sequential, not serial. So if you have 8Gb single rank, the data fills and is pulled from just 1 bank. With dual rank, there's 2 banks, first you pull data from the left, then the right, repeat. To a memory controller that's almost exactly the same as dual channel.

Having 4x DR sticks, in dual channel, is like having 8x SR ram sticks in dual channel or dealing with 8 seperate sources of input on just 2 channels. So the memory controller limits the ram speed, just to get a break and grab a breath.

This was how it was with 1st and 2nd Gen Ryzen, and to some extent 3rd gen, 2x sticks was best, 4x sticks was severely limited, often not getting past 2666MHz.
 

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