CPU Choice for 128GB DDR5

[Mr Technician]

I'm building a top of the line gaming and workstation PC and plan to install 128GB of DDR5 memory in it. At present, this requires me to install 4 32GB (presumably dual rank?) DIMMs, which I understand is problematic at speeds above ~4400 Mhz. However, I prefer having all four DIMM slots full for aesthetic reasons anyway, so waiting for 64GB DIMMs might not help me. I am leaning toward the 13900k because it seems to handle 4 DIMMs better than the 7950X and X3D. Some have had success with 6000 Mhz as in this video: https://youtu.be/_Tnnc9Th13Q.

 

If I want to run this much memory, should I stick with Intel? Also, assuming I get at least an Asus Strix class board, will a better board help me with memory stability? The video I linked above seems to suggest that the Pro Art board works better than other options, but the memory controller is on the CPU.

[Lurking]

On a budget AM5 MB roundup I saw Asus was horrible and couldn't even run 6000. This may be unrelated to your more premium board, though. But I'd look first which MB in general are good with RAM, even if those tests are with less than 128 GB and only 2 sticks. It just goes downhill from there 

 

Ultimately you have to decide if the aesthetics of using 4 sticks trump stability and speed. Maybe there is a market for dummy RAM to fill out the unused slots...  

 

[brob]

Interesting video. Sadly there is no indication of how stable the system is. I noticed those questions have not been answered in the comments.

 

Nor is the kit number provided. Which makes it difficult to replicate the test.

 

If you check the ProArt Z790 Creator memory QVL there are no 4x32GB memory kits. However there are two 4x48GB kits, CMK192GX5M4B5200C38 and CMH192GX5M4B5200C38. The kits are DDR5-5200, so a little slower but 192GB!

 

The same memory kits are also on the more affordable Prime Z790-A motherboard Memory QVL. 

 

[RONOTHAN##]

I do want to point out that Task Manager is pretty unreliable with reading memory frequency and is pretty easy to trick, so while in the video it says it's running at 6000MT/s I wouldn't exactly trust it. Plus the Intel memory controller has this weird problem where it can boot and run some benchmarks at settings 600-1000MT/s higher than what it can actually run with full stability, so even if that 6000MT/s is real I wouldn't trust that it's actually stable. 

 

There are 6 different factors when it memory stability at a max frequency, the motherboard's memory topology, the CPU's IMC quality, the BIOS quality, the RAM sticks themselves, the voltages the board is running, and mounting pressure for everything. From everything I've seen, ASUS's 8 layer 4 DIMM topology is up there as the best 4 DIMM topology you can get currently on LGA 1700 (though the EVGA Classified Z790 might be a bit better, but good luck getting that board and getting it to fit in a system), but it's just copy pasted around on every one of their 8 layer boards. Everything from the Z790-F Strix to the Maximus Z790 Extreme will all end up having the exact same memory support because of that (the ProArt is an 8 layer ASUS board), assuming all other factors are the same. Intel CPUs are also all over the place for IMC quality, there are chips out there that no matter what cannot run DDR5 7200 with just 2 DIMMs, and there are chips out there that can do over DDR5 8000 on those same motherboards. It's very possible that the chip that you end up with will run 4 DIMMs of memory at speeds very similar to what a 7950X would run depending on how unlucky you are. You might also need to do manual voltage tuning to get it to work, depending on how your particular CPU likes voltage values (my personal 13700K wants 1.65V for the VDD2 rail at all times in order to run pretty much anything above DDR5 7000 with single rank memory, while every BIOS I've used trains that voltage to be 1.45V at the settings I'm running). Plus if you're using a contact frame or anything like that it can cause the board to not train properly if you don't have it tightened down just right. 

 

The Intel setup would have a ton of variance in it, so while it might be able to do higher memory clocks on quad rank memory, it still is a nightmare to get working. The AMD system, while it will have a lower max clock it generally either works or it doesn't, so in practice will be a lot less annoying to use. You're probably better off sticking to just 2 DIMMs though with anything DDR5, using those other 2 DIMMs is not very practical a lot of the time even if you think it does look aesthetically better, and if you really need this much RAM you might be better off going for Sapphire Rapids instead

[porina]

Just been poking through the Intel datasheets. It looks like when 4 modules are fitted 13th gen officially supports 4400, down from 5600 with 2 modules. Zen 4 is much worse, at 5200 with 2 modules and 3600 with 4. DDR5 just doesn't like going 4 modules it seems. Of course, these are just official speeds, and enthusiasts can push above those. It does seem like Intel will give the better chance at hitting higher speeds.

 

Other alternative might be to consider the Intel workstation platforms that recently got announced, but they're not going to be cheap. That'll give you more channels offsetting lower speeds if you load it up.

[Mr Technician]

2 hours ago, Lurking said:

On a budget AM5 MB roundup I saw Asus was horrible and couldn't even run 6000. This may be unrelated to your more premium board, though. But I'd look first which MB in general are good with RAM, even if those tests are with less than 128 GB and only 2 sticks. It just goes downhill from there 

 

Ultimately you have to decide if the aesthetics of using 4 sticks trump stability and speed. Maybe there is a market for dummy RAM to fill out the unused slots...  

 

Are there any 64 GB DIMMs on the market, yet?

 

1 hour ago, brob said:

If you check the ProArt Z790 Creator memory QVL there are no 4x32GB memory kits. However there are two 4x48GB kits, CMK192GX5M4B5200C38 and CMH192GX5M4B5200C38. The kits are DDR5-5200, so a little slower but 192GB!

Doesn't the 13900k only run 128GB max?

 

1 hour ago, RONOTHAN## said:

you might be better off going for Sapphire Rapids instead

Given that my choice of 128GB of memory is more for future proofing and because this is still a gaming machine, I think the Xeon line isn't appropriate for me. I could certainly start with 2 x 32GB and upgrade later.

[RONOTHAN##]

1 hour ago, porina said:

It looks like when 4 modules are fitted 13th gen officially supports 4400

It's even worse than that, 13th gen with 4 dual rank DIMMs drops down to 3600 as the max official supported speed. 4400 is the official max speed when just using a 4 DIMM board in general with only 2 sticks. 

https://edc.intel.com/content/www/us/en/design/products/platforms/details/raptor-lake-s/13th-generation-core-processors-datasheet-volume-1-of-2/002/processor-sku-support-matrix/

 

In reality they can do much higher than that, but Intel is very conservative with that spec. 

 

4 minutes ago, Mr Technician said:

Doesn't the 13900k only run 128GB max?

No, they support 24Gb ICs, and they support 4 ranks per channel. That 128GB max was only a thing because initially the largest available die density was 16Gb, so doing the math the largest you could do with the 4 ranks was 128GB. With 24Gb ICs and the same rank limitations, it comes out to 192GB for the max capacity.

 

9 minutes ago, Mr Technician said:

Are there any 64 GB DIMMs on the market, yet?

 

Yes and no. Yes there are 64GB DIMMs that exist, but they're buffered DIMMs and will not work on a 13900K. 32Gb memory ICs that would make consumer oriented 64GB DIMMs a possibility aren't a thing yet, and I haven't heard of anything announced. 

[Winterlight]

What you actually do that need that abnormal amount RAM ?

[Mr Technician]

6 minutes ago, Winterlight said:

What you actually do that need that abnormal amount RAM ?

At this point it's not a strict requirement. I want to run 1-2 Windows VMs for testing software and simultaneously be able to edit 4k ProRes in DaVinci Resolve or Adobe products. 32GB on my current machine is nowhere near enough to do that smoothly. Even software like Jetbrains Rider can eat up 10GB. 64GB is probably enough, but I wanted to go all in- however given the issues with that many DIMMs, I might start with 64GB and upgrade it later.

[brob]

20 minutes ago, Mr Technician said:

Doesn't the 13900k only run 128GB max?

 

That is what Intel and the motherboard spec list. But the Asus memory QVL lists the kits as compatible. Presumably Corsair would not be introducing the kits if there were no motherboards that could use them.

 

[Winterlight]

12 minutes ago, Mr Technician said:

At this point it's not a strict requirement. I want to run 1-2 Windows VMs for testing software and simultaneously be able to edit 4k ProRes in DaVinci Resolve or Adobe products. 32GB on my current machine is nowhere near enough to do that smoothly. Even software like Jetbrains Rider can eat up 10GB. 64GB is probably enough, but I wanted to go all in- however given the issues with that many DIMMs, I might start with 64GB and upgrade it later.

In this case is probably best choose is go for some AMD or Intel workstation grade CPU you have way less problem for that massive amount RAM support. If you use one of this gaming grade CPU even they support that amount RAM you will have another problem that your CPU will be to slow for all your task simultaneous.

[Mr Technician]

12 minutes ago, Winterlight said:

In this case is probably best choose is go for some AMD or Intel workstation grade CPU you have way less problem for that massive amount RAM support. If you use one of this gaming grade CPU even they support that amount RAM you will have another problem that your CPU will be to slow for all your task simultaneous.

Maybe, but I don't think my needs are substantial enough to justify the much higher cost of a HEDT chip if I can feasibly upgrade to 128GB in the future as larger DIMMs become available or memory support improves. I also care about single thread performance for gaming so a Threadripper or similar would hurt me in that area. 

[porina]

35 minutes ago, RONOTHAN## said:

It's even worse than that, 13th gen with 4 dual rank DIMMs drops down to 3600 as the max official supported speed. 4400 is the official max speed when just using a 4 DIMM board in general with only 2 sticks. 

https://edc.intel.com/content/www/us/en/design/products/platforms/details/raptor-lake-s/13th-generation-core-processors-datasheet-volume-1-of-2/002/processor-sku-support-matrix/

 

In reality they can do much higher than that, but Intel is very conservative with that spec. 

Ouch, that puts them at parity with Zen 4 in 2DPC configuration. I wish Intel made that info easier to find. I managed to find a pdf but must have misread the configuration nuance. AMD list it on the CPU page:

From https://www.amd.com/en/products/cpu/amd-ryzen-9-7950x for example

 

Something I forgot to mention earlier, a Zen 4 X3D part could mitigate any reduced ram speeds from going to higher capacities, but not for all workloads.

[Mr Technician]

3 minutes ago, porina said:

Something I forgot to mention earlier, a Zen 4 X3D part could mitigate any reduced ram speeds from going to higher capacities, but not for all workloads.

Is this because of the 3D cache? Otherwise the X3D chip is slower than the non-3D for most multi-threaded workloads.

[porina]

2 minutes ago, Mr Technician said:

Is this because of the 3D cache? Otherwise the X3D chip is slower than the non-3D for most multi-threaded workloads.

Yes, since the cache reduces the pressure on the ram system. It is a complicated tradeoff and not one I can claim to understand myself not having used it. Certainly try to research performance in your expected use cases, but consider what difference the various options might have and in particular if they are significant enough to min/max that hard.

[RONOTHAN##]

20 minutes ago, porina said:

Ouch, that puts them at parity with Zen 4 in 2DPC configuration. I wish Intel made that info easier to find. I managed to find a pdf but must have misread the configuration nuance. AMD list it on the CPU page:

To be fair, Intel's might be hidden a bit more, but they do have more information out there about their memory systems and other parts of the CPU than AMD does. I do prefer Intel's method for it, the more info out there the better, though I will agree it would be nice if you didn't have to know the exact things to google in order to find it, maybe put a link on the Intel Ark page to all the related PDF downloads.  

 

I will point out though that Intel has a tendency to be much more conservative about their max memory speeds than AMD is, so even though they're officially on parity with each other Intel's is still better. 

[Mr Technician]

I'm starting to lean more strongly toward the 13900k with 64GB of memory to start. I don't like being locked to LGA 1700 (no upgrade path) but I doubt I will be getting a new CPU in this build at any point anyway.

 

My other consideration is how well Hyper-V will handle big-little. From what I can tell the scheduler is smart enough to make use of both core types when running a VM.

[brob]

If you are considering Intel, a DDR4 build could reliably handle 128GB of memory.

[Mr Technician]

13 minutes ago, brob said:

If you are considering Intel, a DDR4 build could reliably handle 128GB of memory.

True, but I think the trade off for speed wouldn't be worth it. I will need to check benchmarks.

[RONOTHAN##]

6 hours ago, Mr Technician said:

True, but I think the trade off for speed wouldn't be worth it. I will need to check benchmarks.

128GB of DDR4 is aout the same performance of 128GB of DDR5 because the speeds end up so similar, and 128GB of DDR4 is a lot less annoying to run. There are some features on DDR5 boards that you can't get on DDR4 boards, so it can still on occasion make sense to go DDR5 still, but going DDR4 is likely to be the better solution as 3600 CL16 isn't that impossible on 128GB of RAM if you bump the system agent up. 

[cemsterland]

Personally I have allergic reaction to the previous technology

"I'm sorry for barging in like that, but I have a very similar predicament."

 

I shared my problem in various forums, but only one of them proved to be fruitful.  (Tom's)  

 

My objective was to construct a modest AI workstation that boasts an Intel Core i9-13900KS, an ASUS ROG Maximus Z790 Extreme, and a Nvidia RTX 4090.

Although, the promised 128GB DDR5 RAM capability feels more like a fallacy than a reality, since there are no 128 GB kits available at all...

 

However, more and more motherboard manufacturers starting to include 4x48GB kits in their respected QVL... MSI, Gigabyte, Asus...

 

And the reason for this perhaps is this;

 

I am told that, in fact the 13900K and its series, are "unofficially" supports 192GB DDR5 RAM.

 

And they have done successful tests with some of the motherboards, without even BIOS alteration to prove that.

 

So, I am very hopeful, with near future BIOS updates we might get 192GB even with higher clocks... 

I am looking forward to take full advantage of the LGA1700's RAM capacity with my proposed configuration.

 

I have been in contact with all the involved companies.

 

Intel doesn't want comment on anything other than 128GB. 

 

I asked  them then tell me how did you achieved 128GB? What components did you you tested to claim this mysterious 128 GB?

 

I got no straight answer to that...

 

Asus, is another story. Unless you have a registered product, you don't get to open a channel with Tech people, and the available alternative which is sales rep,  does not help.

 

I am however, going to have a landline conversation with ASUS, and hopefully that will be with a Tech, and I will have some clarity...

 

It's important to note that Corsair's technical support is of high quality. The Tech team goes above and beyond in their efforts to assist you.

 

The only useful info and feedback came from Corsair.

 

 

[Mr Technician]

It's interesting that you mentioned this because I have been looking at the 96 GB kit from Corsair and a good alternative. I'm also likely going to go with the 13900k but that remains to be seen for the next week as I nail down my water cooling parts.