cancel
Showing results for 
Search instead for 
Did you mean: 

Is quad channel memory a better pick than dual channel?

Perko
Level 8
Yes?
No?

Maybe so?

SS
Case Labs S8
ASUS X99 Rampage V Extreme
i7 5960X
EKWB XTX360 kit +1 XTX360 & XTX240
10x MassCool fans on a Lamptron FC5 6 Channel 30W LED Fan Controller V3
32GB Geil Potenza 3000Mhz
2x Samsung 840 EVO 1TB
WD 7,200 Hybrid 2TB
ASUS Blu-Ray RW
Gigabyte 980Ti G1 EKWB full block
Acer XB270HU monitor
EVGA 1200 P2
Razor 7.1 phones, Death Ader & Ultimate KB
Madcatz Panther XL SteveO modded
269 Views
20 REPLIES 20

Korth wrote:
The internal memory controller (iMC) in a Haswell-E proc is designed to address up to 4 channels (and up to 64MB) of DDR4-2133. Quad-channel actually means there's four discrete memory controllers working in parallel, each is tasked to addressing the memory occupying one electrical DIMM. Just like multiple CPU cores work in parallel but (ignoring things like HyperThreading) each can only run a single computing pipeline.

The R5E happens to splice the four electrical DIMMs into two physical slots each, so it supports a total of 8 physical DIMMs (pretty much exactly what Intel designed into X99 and Haswell-E).

Populating half the channels with two DIMMs each forces two of the iMCs to work almost twice as hard while the other two iMCs are idling or tasked to supporting functions, it's less efficient than populating all four DIMMs so the load is balanced across all four iMCs. "Less efficient" referring to overworked iMC circuitry needing a slight voltage bump (and thus running a wee bit hotter) as well as a higher incidence of signalling errors and "traffic jams" on the saturated data bus (which slightly increases overall latency). The iMCs themselves are apparently internally hardwired directly into discrete pairs of CPU cores, and needlessly re-routing tons of electrical signals across your processor die accomplishes little more than turning power into heat. You should want all that data sitting around in your RAM to flow in and out of all your processor cores at the same rate so there's no bottlenecks and no hotspots, less strain on the iMC means more headroom to cool off or overvolt and strain some other piece of silicon, lol.

And then there are Double-Sided DIMMs. As the name implies, these are DIMMs which have memory chips soldered onto both sides of the PCB. The DIMM itself has yet another dedicated memory controller chip which translates all this memory into a single logical DIMM. This unavoidably adds a teeny bit more latency to all memory functions on the DIMM. Server RDIMMs are typically capable of reading and writing different memory segments simultaneously (which, along with greater memory capacity, generally outweighs the disadvantages of added latency), but consumer UDIMMs (used by X99 mobos like the R5E) are "cheap" stuff which generally lack this capability. The sad truth is that UDIMMs are often Double-Sided because they allow manufacturers to easily pack on twice the capacity at same speed and lower cost (bulk low-density memory chips cost a lot less and are easier to bin than bulk high-density memory chips) - so the majority of 32GB+ DDR4 kits these days are made of DS DIMMs.

Ideally, you'd want to populate each of your four DDR4 channels with one Single-Sided DIMM. There's no logical difference between four Single-Sided DIMMs or four Double-Sided DIMMs or eight Single-Sided DIMMs, the processor will still "see" four DIMMs either way, although two double-loaded channels will be worse than four single-loaded channels and eight physical DIMMs will tend to have more complex and slightly slower timings than four physical DIMMs. Any real difference would largely be based entirely on the capabilities of the iMCs built into the X99 platform vs the capabilities of the memory controllers onboard the DIMMs. And, unless you end up with garbage parts, the differences would be insignificant - you might actually be able to isolate them in benchmarks (and they do all add up) but you would never notice any difference in real usage. If you're planning on some hard overclocking then it can't hurt to work within the limits built into all your hardware.

Assuming otherwise identical specs, I would just grab whichever of the two kits costs less or looks best or whatever. Don't bother planning on keeping half your DIMM slots open for future memory upgrades because you can't really mix DDR4 kits anyhow, you'd still have to yank out all of whatever's already installed if you want to increase capacity later.
Server folks might advise the opposite, but they're primarily interested in server platforms which work a little differently (what we call "Double-Sided" they call "Dual-Ranked", and they just love RDIMMs which pack on more and more Ranks because they gain capacity and performance advantages from it, while consumer platforms tend to gain greater memory capacity at the cost of greater latencies which impact performance).


Hey,

That's a very nice answer,

Nax
Cpu : Intel 5930K@4.25ghz@1.2v / Cache @4.25ghz@1.20v
Cpu Cooler : Corsair H100i
Case : Corsair 780T
Memory : G.Skills 32GB DDR4-3200mhz CAS 15-15-15-35-1T@1.370v
Motherboard : Asus Rampage V Extreme (BIOS 3504)
M2 : Samsung 950 Pro NVME 512gb (Gaming)
M2 : SSD1 : OCZ RD400A 128gb (windows)
SSD1 : Crucial MX100 512gb (data)
Gfx : EVGA Titan X w/ 980 Hybrid Cooling AiO Liquid Cooler
PSU : Antec HCP-1000W
Monitor : Asus RoG Swift

Avenger411 wrote:
Hey,

That's a very nice answer,

Max


I concur with that, Max. Korth is a master who explains his perspective, which always seems to be more actual than theoretical, in minute detail. I keep trying to raise his rep, but the forum will not yet let me do so again.

Oh, and I bet he types really fast, too, which does not hurt.
¡¡¡ I__ju$₮__₩₳₦₮__₮☮__₱£₳¥__₮h€__₲₳₥€__₩i₮h☮u₮__i₮__hi₵₵u₱i₦₲,__₱l€₳$€ !!!

Arne_Saknussemm
Level 40
Korth!

That post was no so dimm! 😉

Nice one!

OP....

Don't try to understand the architecture and limitations of your system and weigh up latencies, channels, frequency, single sided, double sided, ECC, non.... etc.

Buy by colour or the "MOAR is betah!" rule and if it has flashing lights then get it even if it's DDR2!!!

Korth
Level 14
My work involves embedded systems and programmable microcontroller parts. I'm not seriously expert in PC technology but at the bottom level (where bits and bytes and clocks and pins and volts are all very carefully tallied) a PC is just another complex machine built out of simpler machines which operate on the same fundamentals.

I don't have any secret Intel info, I just know how other microcontrollers and microprocessors work with memory and how I would build a working PC from existing PC parts. I learn odds and ends from IP hardware nerds. I experiment with and mod and prototype my own hardware from time to time (I'd appreciate help scratch-building a UEFI/BIOS from anyone else out there who's replaced their R5E ROG chip with a juicy ARM, lol). There is really only one way to meet spec at a price point so that tends to always be the way things get done.

No reps please, I do pretty well with platform overclocks and can hold my own on a few games but I ain't truly ROG stuff, lol.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams

[/Korth]

Hardliner
Level 11
Be that as it may, regardless, your valuable input is always appreciated--thank you.
¡¡¡ I__ju$₮__₩₳₦₮__₮☮__₱£₳¥__₮h€__₲₳₥€__₩i₮h☮u₮__i₮__hi₵₵u₱i₦₲,__₱l€₳$€ !!!

Perko
Level 8
OK.

So using 4 single sided matched sticks in the red slots means a greater chance of a higher stable clock speed...... if I read that right.

SS
Case Labs S8
ASUS X99 Rampage V Extreme
i7 5960X
EKWB XTX360 kit +1 XTX360 & XTX240
10x MassCool fans on a Lamptron FC5 6 Channel 30W LED Fan Controller V3
32GB Geil Potenza 3000Mhz
2x Samsung 840 EVO 1TB
WD 7,200 Hybrid 2TB
ASUS Blu-Ray RW
Gigabyte 980Ti G1 EKWB full block
Acer XB270HU monitor
EVGA 1200 P2
Razor 7.1 phones, Death Ader & Ultimate KB
Madcatz Panther XL SteveO modded

Perko wrote:
So using 4 single sided matched sticks in the red slots means a greater chance of a higher stable clock speed...... if I read that right.

Yes, a single 32GB kit made from 4x8GB Single-Sided DIMMs would be best for the R5E, populating the four red DIMM slots (A1/B1/C1/D1). This offers quickest latency and maximum stability at minimum volts, it feeds all of your CPU cores evenly and would tend to simplify (and help stabilize) all overclocking efforts which involve the RAM and processor. A single 64GB kit made from 4x16GB Single-Sided DIMMs would be ideal for the X99 platform (assuming Single-Sided 16GB DIMMs ever become available for consumer platforms, they are currently all Double-Sided).

The R5E firmware can now address 128GB (8x16GB) and some other X99 mobos can now address even more, these mobos all have onboard memory controllers (a nod to the foresight of the R5E engineers). Every hardware memory controller (or other part) the logic has to run through will increase overall signal latency and decrease overall stability, lesser parts also impose performance thresholds and better parts quickly inflate price. Addressing memory through firmware memory controllers (without supporting hardware) is also possible but it's far too slow and complicated to be practical for extreme memory frequencies.

DDR4 uses an advanced point-to-point architecture which greatly reduces the impact of latency anyhow, it steals a lot of refined server-tech that's been in use for half a decade. The traditional memory timing formula describes DDR3 well but is largely inaccurate for DDR4. I would choose a DDR4 kit which fills each channel with a Single-Sided DIMM first, then focus on raw frequency, worry about latency spec last.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams

[/Korth]

Hardliner
Level 11
I hope someone who knows for sure answers this, but I think if you only had two sticks, you would just use the 'red' RAM slots. Since you are using 4 sticks, though, I am pretty sure you use both the 'red' and the 'black' slots to the right side of the CPU and leave all four slots (red and black) to the left of the CPU open. Look at the following pic:

53164

The above pic comes from this link: https://www.asus.com/us/Motherboards/RAMPAGE_V_EXTREMEU31/
¡¡¡ I__ju$₮__₩₳₦₮__₮☮__₱£₳¥__₮h€__₲₳₥€__₩i₮h☮u₮__i₮__hi₵₵u₱i₦₲,__₱l€₳$€ !!!

Arne_Saknussemm
Level 40
I don't see how you can get that from that diagram

Best to fill first and second priority slots and then third and fourth? So all red first.......

Then there's always the manual
53166

Hardliner
Level 11
Okay, I am glad you answered. Now I know that I was not reading the diagram right.
¡¡¡ I__ju$₮__₩₳₦₮__₮☮__₱£₳¥__₮h€__₲₳₥€__₩i₮h☮u₮__i₮__hi₵₵u₱i₦₲,__₱l€₳$€ !!!