DDR4 Memory - Bandwidth, Latency, Quad vs Dual Discussion

[EarthDog]

Not 100% sure, but i believe so.

 

[wingman99]

Aaaand I'm lost.

Think of it this way ganged HDD is Raid 0 and unganged JBOD (just a bunch of disks). The memory works like these HDD setups.

The definition of gange

arrange (electrical devices or machines) together to work in coordination.

With the start of dual channel on the PCs they used ganged. Example dual channel, two memory channels striping 64bit of data across 128bit for twice the speed.
So in the past AMD had a option to change from gange to unganged. Intel does not have memory controller option, they just run unganged. Example dual channel runs two independent memory channels each sending and receiving 64bit with bus.

 

[UltraTaco]

Which one is faster? I'm running twin chanel, but I can't pick either option

Raid vs jbod tech can be both fast depending on how you arrange data on jbod

 

[Alaric]

I got it, I just never heard the term used relative to drives.

 

[EarthDog]

Which one is faster? I'm running twin chanel, but I can't pick either option

Raid vs jbod tech can be both fast depending on how you arrange data on jbod

depends on the test... both similar. Lots of testing if you look. It makes sense you cant pick anything as, again, its an AMD term and functionality....you have an intel x58 based system.

I got it, I just never heard the term used relative to drives.

me either.

 

[wingman99]

Which one is faster? I'm running twin chanel, but I can't pick either option

Raid vs jbod tech can be both fast depending on how you arrange data on jbod

You don't have a choice Intel runs unganged separate memory channel for individual 64bit memory channels. The manufactures don't have a choice now because the separate memory channels support multi-threading with multi-core processors with increased performance gains.

 

[Alaric]

the separate memory channels support multi-threading with multi-core processors with increased performance gains.

That's their story and they're sticking to it. LOL (Probably true, too. I was just poking fun at the presumed lack of objectivity from the source.)

 

[(G{in}[AK)TION]]

TL;DR

Quad channel would have more latency and less bandwith than dual channel but probably by a little difference.

The memory sticks running in quad channel are on both sides of the processor where with dual channel they are all together in one spot close together.

From what i am seeing here, the only advantage quad channel boards have over dual channel boards is support for more memory.

 

[Alaric]

Yeah, other than some specific applications, quad channel doesn't offer anything tangible (outside of some benchmarks) for the average user except bragging rights.

 

[mackerel]

Quad channel would have more latency and less bandwith than dual channel but probably by a little difference.

The memory sticks running in quad channel are on both sides of the processor where with dual channel they are all together in one spot close together.

From what i am seeing here, the only advantage quad channel boards have over dual channel boards is support for more memory.

The big selling point of quad channel is more bandwidth over dual. A doubling, strangely enough. Capacity is a side effect. Logically I think it shouldn't affect latency, but I don't have evidence either way.

For my use cases, which are about worst case when it comes to ram bandwidth, I'd rate dual channel ram ok to 4 Intel cores, and quad channel would scale to 8 cores. Look at the techspot/hardware unboxed review of the latest threadrippers. While I don't have a way to verify their results, they claim the highest core count model is choked in some workloads due to the limited bandwidth available, although personally I think it is also in part due to the multi-die approach and additional limitations that brings compared to monolithic designs.

 

[EarthDog]

TL;DR

Quad channel would have more latency and less bandwith than dual channel but probably by a little difference.

The memory sticks running in quad channel are on both sides of the processor where with dual channel they are all together in one spot close together.

From what i am seeing here, the only advantage quad channel boards have over dual channel boards is support for more memory.

Not sure on latency, but bandwidth certainly increases significantly...not a little difference.

 

[wingman99]

Multi channel performance really comes down to the program running. If the cores need most of the same data like blender then increased independent channels will not improve performance to a great extent. Where as 7-zip Compression of jpg files greatly benefits from 1 channel to 2 channels = 21% performance increase and from 1 channel to 4 channels = 39% Performance increase.

 

[(G{in}[AK)TION]]

I went back to go check and you are right.

GIGABYTE X299 DESIGNARE EX
https://www.newegg.com/Product/Product.aspx?Item=N82E16813145050 >>advertises support up to DDR4-4400Mhz

ASUS ROG RAMPAGE VI EXTREME (x299)
https://www.newegg.com/Product/Product.aspx?Item=9SIA6ZP6JN1496 >> Advertises support up to DDR4-4200Mhz

GIGABYTE X299 AORUS Gaming 7 Pro
https://www.newegg.com/Product/Product.aspx?Item=N82E16813145079 >> Advertises support up to DDR4-4400Mhz

and then looking at these dual channel boards

ASUS ROG Maximus X Code (z370)
https://www.newegg.com/Product/Product.aspx?Item=N82E16813119045&ignorebbr=1 >> Advertises support up to DDR4-4133Mhz

ASUS ROG Maximus X Formula (z370)
https://www.newegg.com/Product/Product.aspx?Item=N82E16813119046&ignorebbr=1 Advertises support up to DDR4-4133Mhz

GIGABYTE Z370 AORUS GAMING 7
https://www.newegg.com/Product/Product.aspx?Item=N82E16813145076&ignorebbr=1 Advertises support up to DDR4-4133Mhz


As far as latency goes, not cas latency, probably affected probably not.

themoreyouknow.jpeg

 

[EarthDog]

A little confused why you listed board memory support...it really has nothing to do with bandwidth except to display the board supports the multiplier.

Asus Apex (z370) 4500+ - https://www.asus.com/us/Motherboards/ROG-MAXIMUS-X-APEX/

Asrock taichi (z370) 4333+ - https://www.asrock.com/mb/Intel/Z370 Taichi/index.us.asp

Memory support on boards is not related to dual/quad channel bandwidth. So yes, we are right, but for different reasons than you posted.

Also, good luck getting memory much past 4k on x299. The dual channel coffee lake platform has a much easier time doing so. Dual channel is less stressful on the IMC than quad.

 

[(G{in}[AK)TION]]

So then i was right to think that quad channel is, at least kind of, slower than dual channel?

 

[EarthDog]

Nope. We reading the same thread?

Quad channel is faster... when the bandwidth can be used.

 

[(G{in}[AK)TION]]

Enlighten me

How exactly is quad channel faster than dual channel? You say that dual channel can go up to higher frequencies than quad channel and dual channel is much easier on the IMC than quad channel is.

 

[mackerel]

If we have multiple modules running at the same speed, if you have more channels of them, you get more aggregate bandwidth from the number of channels.

If you look at ram clock speeds, dual channel may be easier to hit higher speeds as it may be less demanding than trying to do same on 4 channels. Overclocking mobos may go a step further, and only give you two ram slots, as having more than one module per channel can make it harder to get the highest speeds.

Total bandwidth is proportional to clock speed multiplied by number of channels (and some other minor factors). More channels just gets you a lot more bandwidth more easily than trying to increase clock can.

 

[EarthDog]

At the same clocks and cas latency quad is much faster than dual, bandwidth wise. That said if the bandwidth goes unused, its akin to hooking up a firehose to a spicket on your house instead of a fire hydrant.

Edit: what mack said.

 

[wingman99]

DDR4 2666：21.3 GB/s for single channel. DDR4 2666 with dual channel if the data needed is coming from the two individual channels then the total speed of the two separate data sets will be 41.6 GB/s. If the two separate data sets needed by the processor are on the same channel then the speed will remain 21.3 GB/s. That is some of the reason including all the memory primary timings why memory benchmarks are so inconsistent with reboot and run after run.