Question on RAM


#1

My question is about RAM speed, not capacity.

Does RAM speed (frequency and latency) makes significant difference on 3D applications in general?

Thank you very much, any input is welcome :slight_smile:


#2

I don’t think there is really a perceptible difference because the bottleneck is the processor speed. What is the difference in speed between the fastest and slowest RAM anyway?


#3

Apparently if the computer isn’t bottlenecked by the CPU or GPU, doing a comparison between 2133 Mhz and 3200 Mhz DDR4 RAM (same latency), the difference seems to be around:

Gaming: 1 to 10 FPS tops (average)

Video Editing / Rendering: I honestly found little to no info on RAM speed, the few I found showed a negligible difference (seconds), I will edit this whenever I get more info.

3D applications: not much info, will edit too.


#4

It depends on the application, and how many RAM read/write operations it needs to do per second.

If your application needs to access RAM a lot and your CPU or GPU has to wait around doing nothing until the data arrives, then yes, slow RAM will slow the application/computer down.

In a 3D app, it would depend on the 3D function being used.

For example, if you have the positions, directions, velocities and other properties of 10 million particles in RAM, and the CPU needs to read those millions of data points from RAM to calculate the next step in the simulation, and then wait for the new values to be written back to RAM, and then read the new values again, then that waiting time will obviously slow down the rate at which the particle simulation calculates. This assumes, of course, that the CPU does what it does so fast that it keeps waiting for new data to arrive.

So if you have a 24 Core CPU capable of processing 100 million particles per second, but RAM can only handle read/writes for 50 Million particles per second, your simulation speed will slow down by 50%.

In video editing it is the same deal. For example, 4K UHD HDR video at 30FPS amounts to 250 Million 3 x 12bit RGB pixels per second being processed.

If your RAM can only pipe 200 Million pixels per second into the CPU/GPU, rather than 250 Million pixels, then stuff like compressing that 4K UHD video may run 20% slower, and you may not be able to playback the 4K video at 30 FPS - you’d get 24 FPS playback instead. Obviously video at 8K UHD or at 4K 60 FPS or higher - gameplay captures for example - make this problem worse.

How severe the slowdown is would depend on the RAM speed.

Basically, if your CPU/GPU needs more data reads/writes per second than RAM can feed it - for applications that need to run in realtime at high FPS for example - slow RAM can indeed form a bottleneck that slows everything down.

How much depends on the RAM speed and type, CPU/GPU speed, and how many read/writes per second are involved for that particular application.


#5

Thank you for taking your time to explain all that! :slight_smile:


#6

If there are 2 RAMs with the same DDR (ie. say DDR3) - are they different in any way? Is it worth it buying the more expensive one??


#7

In short: no

But I do still recommend not getting simply the slowest one. Get something in the middle.


#8

Makes a big difference with simulations that save out huge caches - fluids, fire, smoke etc.


#9

Check your motherboard specs.

Ultimately, It may technically support something like DDR4-3200, but bottleneck you at 2666 instead. It may be utterly worthless getting anything faster. I found this out in doing some research for my new x299-based rig. You might also want to be careful of latency ratings. There doesn’t seem to be a true standard. Just because you see a CL15 don’t automatically assume that it’s going to perform any better than a CL16. It might. It also might not. Every manufacturer’s RAM is different.

IMO, what you want much more than speed with RAM is stability. Some RAM craps out easily, trading speed and overclocking flexibility for accuracy. When you’re doing this sort of work, imo, you want accurate writes and reads. Fast is nice. Reliable is better. From my research, the top two in this regard tend to be Corsair and Kingston. Other brands like G.Skill & Patriot might perform a shade faster in certain circumstances, but they’re not as reliable.

While you’re at it, unless you’re building a rig that’s meant to be flashy, avoid RAM with RGB lighting. It’s an unnecessary added expense, especially if your case doesn’t have a window or tempered glass panel.

One final thing. Beware of those RAM heat spreaders. While they serve a purpose, some are large enough where they affect the RAM’s installation or clearance from other parts. Corsair modules generally seem to be fine across a wider variety of case sizes and motherboard form factors.


#10

What he said.
I don’t often do this, but this question about RAM speed etc. pops up ever so often and people are quick to point out any numbers of improved performance, when the reality is much simpler.
A very small speed increase is not worth the potential trouble. Buy the specs required for the chipset and CPU, buy a reliable brand, done. And yes, those coolers usually create more problems then they solve.