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Difference between 2 and 4 RAM sticks


#1

I can’t for the life of me figure out whether to buy 2x16 GB RAM sticks or 4x8.

I’m fairly certain I heard Wendell say in a recent youtube video that if you could get the same amount of RAM on 2 sticks, that would be preferable over 4 sticks.

However, when I browse for which RAM to buy, I see that the 8 GB RAM sticks have better timings compared with 16 GB RAM sticks.

So basically: would 2x16 GB RAM sticks perform better than 4x8 GB RAM sticks even though the latter have tighter timings? (Say CAS 17 compared to CAS 16).

Also, if I were to buy 2 additional 16 GB RAM sticks at some later point, for a total of 64 GB, would my performance suffer?

In my specific scenario, I’m buying a Ryzen 2700X with an Asus Crosshair VII Hero (X470).


#2

General rule with Ryzen is always to prefer 2 sticks over 4.

If you want 32GB get 2x16GB. 2x8GB will have better timings/speeds though.


#3

the more physical chips on the dimm, the denser the routing and the worse signal integrity you get. Or, the same # of chips with higher capacity means each line is addressing more of the ram by each, which means you can only access the same amount at once despite having double the capacity.

there’s also the matter of memory channels, where more lower capacity kits may exploit more bandwidth, because you have to physically populate the slots to enable dual/quad channel bandwidth.

The third factor that plays into this is die rank, which is a bit harder to explain. essentially, each rank on the bus is 64 bits wide, and maps out a block of memory that can’t be accessed at the same time as any other bank.

Dual rank kits are cheaper, but generally lower bandwidth and slower with less OC headroom because less memory is addressable at the same time, and routing x8 connections is harder than routing x4 (single rank)

Then there’s the memory controller to consider. Some platforms perform fine with lots of dimms, others are more picky

so the tl;dr is that lower capacity dimms perform better if single rank in terms of speed, timings, and OC, but there are some circumstances where you might just want more capacity


#5

Alternative logic:

If you need/want 32 GB today, chances are you may need/want 64 GB in the future within the life of this machine.

Go for 2 sticks.

Don’t obsess over memory speed TOO much, yes it makes a (small) difference in benchmarks, but having the ability to have 2x the RAM down the track will make much more difference to your actual use of the machine.

2c.

edit:
yes. 4x dual rank sticks for 64 GB may need you to run lower timings. so performance will maybe be impacted. but performance won’t be impacted as badly as running your apps/data out of SWAP :smiley:


#6

I suppose that’s technically true, but I hear Ryzen in particular likes as low delay on its RAM as possible, and that it can make a significant difference when it comes to the minimum FPS / 97th percentile in games.

That might be less of an issue in later Ryzen iterations though, perhaps I can have my 64 GB RAM and eat it too in a couple of years.


#7

I’m running 2 dual rank, non-b-die DDR4-3000 sticks at 2866 just fine (2700x on x470 taichi). literally all i did is pick 2866 from the bios.

Performance is great. I’d go for the 2 sticks. I’m not saying there’s no benefit, but it’s not like your performance is going to totally tank.


#8

With the newest motherboards together with the 2x00 series Ryzen I guess there could well be some ideal case where 4 x 16GB sticks could run stably at reasonably higher speeds. For what I have seen though, fully populated slots with dual rank RAM tends to still be quite the limiter when it comes to the practically stable clock speeds. (something I also encountered while overclocking my Haswell Refresh build a couple of years ago)

As a simple yet somewhat outdated example, take my system. An early adopter with a Ryzen 7 1700 and a Asus Prime X370 Pro motherboard I splurged on RAM and got a 2x2 kit of the same 16GB 2666 MHz pretty bog standard Corsair DDR4 that has since gone out of market. For over six months I fought with different BIOSes, manual timings, and voltage tweaks to get 4 x 16 to run at 2666, but what looked stable for a couple of days even during stress test could start acting up the next week. It was a constant back and forth, while it never leaving the back of my mind what a mess unstable RAM can cause even when not outright crashing. (silently corrupted file transfers, yay)

I finally gave up on using 4 x 16 GB and tried instead to get the most of out 2 x 16 GB. Using the Ryzen RAM Timing calculator together with some program that helped identify the exact make up of my RAM sticks, I saw indications that there was some potential for overclocking the memory while also tightening the more esotheric sub timings. So now after a month or so I at least have 32 GB running at 2866 MHz with slightly better timings than what the default XMP suggests for 2666. Edit: make that 2933 now.

Though this video talks about ECC memory in particular, it is relevant here as well:


#9

Ryzen 7 1800X, C6H, 4x16GB @ 3333: https://www.overclock.net/forum/11-amd-motherboards/1635742-ryzen-memory-support-duel-rank-2-x-f4-3200c14d-32gtz-kit-64gb.html

Interestingly, getting the same result with a 2700X and X470 motherboard seems to be more difficult.


#10

So hey, after researching this a little I get the sense that RAM stability depends a lot on the motherboard. Is there any consensus on what’s currently the “best” X470 motherboard for RAM stability at higher clocks with, say, a Ryzen X2700?


#11

I think that’s where Asus takes the lead. Its BIOS has the most tuning options, and “The Stilt’s” presets help get “tuned” out of the box experience for certain popular single rank sticks. I hope they also make some presets for dual rank modules eventually.

The C7H seems to be the enthusiast board when it comes to overclocking. There is an active community on OCN constantly pushing limits, often just for its own sake.


#12

essentially anything other than the top end boards run garbage subtimings at seemingly random settings.

MSI/GB is supposed to be worse anectodally


#13

i would just throw in what buildzoid and the like say about 2 vs 4 sticks.
(assuming both setups are dual channel only of course)

2 sticks is less stress on your memory controller, which means easier overclocking/more stable.
so clocks, that u might get stable on 2 sticks may be a nono on 4 sticks.

please do your own research about it, but i thought i throw out the overclocking concern.