Ryzen 9 7900 compatibility with RAM

[Thill3]

I am settling in on parts for a new computer build. My main use case is Convolutional Neural Networks and then simpler machine learning/artificial intelligence applications.

 

I'm planning on a Ryzen 9 7900 CPU because it should last for a while, it has 12 cores (24 threads), and AMD has some advantages over Intel for data science applications.

 

I'm concerned that I may be planning the wrong RAM though, so I'm looking for input. Newegg says that the processor works with DDR5 5200 and can only handle up to 128GB of RAM.

 

Does that mean that if I start with Corsair Vengeance 2x48 DDR5-5600 then the CPU is going to limit it to 5200 out of the box?

And if I want to upgrade my RAM in the future then will I be able to use another set of 2x48 DDR-5600? Or will I be effectively limited to an additional 2x16 (or just replacing with 4x32)?

 

 

[RONOTHAN##]

13 minutes ago, Thill3 said:

Newegg says that the processor works with DDR5 5200 and can only handle up to 128GB of RAM.

The 5200 figure isn't the whole picture, and the 128GB figure is out of date. 

 

The 7900 officially supports a maximum of 5200MT/s, but it also supports memory overclocking and in practice every Ryzen 7000 series chip should be able to do at least 6000MT/s. As for the 128GB figure, the 7900 was released before 48GB DIMMs were a thing, so it would have been weird for them to say that it supports 192GB of RAM when there was no physical way to install that. It will recognize and run with 192GB of RAM installed, though odds are you'll be limited to speeds below 4400MT/s due to 4 high capacity DIMMs being very difficult for the memory controller to drive. It should also support 256GB of RAM once the 64GB unbuffered DIMMs release to the general public later this year, though again with similar speed restrictions. 

 

 

One thing I'd like to mention though is that if you are looking at the 2x48GB kits, try to avoid the ones rated for 5600 CL40, 6000 CL40, and all the other high CAS latency kits. Those kits are usually Micron based, and those can have weird stability and compatibility issues depending on the motherboard and BIOS revision. The SK Hynix based kits (the ones with a low CAS latency) are not that much more up front and are better for overall stability and performance as well. 

https://pcpartpicker.com/product/jn26Mp/gskill-ripjaws-s5-96-gb-2-x-48-gb-ddr5-6400-cl32-memory-f5-6400j3239f48gx2-rs5k

That is currently the cheapest SK Hynix based kit in the US, though just keep in mind that you will not be able to just enable XMP due to 6400 being a bit too fast for most CPUs, so you'll want to lower the speed to 6000MT/s just in case. 

[Thill3]

2 hours ago, RONOTHAN## said:

in practice every Ryzen 7000 series chip should be able to do at least 6000MT/s

Does that mean i will have to learn to do the overclocking manually? I was really hoping for things to work properly out of the box or with minimal configuring.

 

2 hours ago, RONOTHAN## said:

try to avoid the ones rated for 5600 CL40, 6000 CL40, and all the other high CAS latency kits.

Is there a specific threshold number where the frequency is considered "high" and then a slightly lower number is considered "low", or is it kind of a spectrum (like so many other things)?

 

 

2 hours ago, RONOTHAN## said:

all the other high CAS latency kits. Those kits are usually Micron based, and those can have weird stability and compatibility issues depending on the motherboard and BIOS revision

Is there any way to know beforehand whether problems will arise? I'm trying to limit the spending on this project where i can, so if i don't have to drop another 50 or 60 dollars on RAM with higher speeds than I'll probably use would be ideal.

MB plan is Gigabyte B650 EAGLE  AX ATX Motherboard - https://pcpartpicker.com/product/CvcgXL/gigabyte-b650-eagle-ax-atx-am5-motherboard-b650-eagle-ax

As far as I can tell it is the case that the MB only takes non ECC ram, and that is the kind that the 2x48 set i picked is.

 

 

So i guess the overall question is - what set of RAM sticks will be a good start for my MB given that I expect to be doing a significant amount of work with large datasets (often of images) so that holding my whole dataset in memory may have advantages over moving it in and out?

[RONOTHAN##]

26 minutes ago, Thill3 said:

Does that mean i will have to learn to do the overclocking manually? I was really hoping for things to work properly out of the box or with minimal configuring.

No, auto settings should get 6000 to work. It's just enable XMP/EXPO and you're done, or with that one kit I linked, enable XMP, manually lower the memory speed to 6000, and you're done. If you don't enable XMP, yeah, you'll be limited to DDR5 5200. 

 

26 minutes ago, Thill3 said:

Is there a specific threshold number where the frequency is considered "high" and then a slightly lower number is considered "low", or is it kind of a spectrum (like so many other things)?

This method is not perfect, but the one I use is if the data rate divided by the CAS latency is below 180, it's not Hynix based. I.E. 6000/32 = 187.5, therefore it's Hynix based, but 6400/36 = 177.7, therefore it's not Hynix based. 

 

31 minutes ago, Thill3 said:

Is there any way to know beforehand whether problems will arise? I'm trying to limit the spending on this project where i can, so if i don't have to drop another 50 or 60 dollars on RAM with higher speeds than I'll probably use would be ideal.

Fair enough. Most of the issues with these kits are just that motherboard manufacturers as a whole have put little effort into getting the BIOS optimized for them, and therefore you can get some weird issues on some BIOS revisions. The worst I've seen is it booting the full 5600 and getting to BIOS, but blue screening immediately even at 3600 despite working fully well on an Intel board. From what I know, most of those issues have been fixed, though when you're going to be spending ~$300 on a memory kit anyway, an extra $50 to make sure you won't have issues is worth it IMO.