Question CPU 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)?

 

[geofelt]

Ryzen depends on fast ram for best performance.
For your selected motherboard, look at the ram QVL tables for the R9-7900 processor.
It will list exact part numbers that have been tested on that motherboard.
You will want the strongest compatible ram that your wallet will pay for.
Not all extant ram has been tested. If you fancy a different ram maker, they will have a ram selection table from which you can pick a kit that works for you.

Motherboard and cpu ram speeds are the default speeds at which the ram will boot into bios.
Generally an irrelevant spec since all ram will have a low speed default that lets you boot into the bios.
Once there, you specify the speeds and settings you want.
The usual way is to tell the bios to extract the xmp or expo settings that are embedded in the ram.

Ryzen (or intel for that matter) processors operate in dual channel only, regardless of 2 or 4 sticks.
Plan on buying all your ram needs up front. Adding ram later is likely not to work properly. Ram must come in a single kit.

If you need more ram later, plan on selling the old and replacing with a new kit.

What is the app that you plan to use?
Many apps will depend on the power of a single master thread.
Even multithreaded apps may depend on the single master thread.
Read about amdahl"s law:
https://en.wikipedia.org/wiki/Amdahl's_law

I mention this because Intel 14700 or 14900 may be stronger in single thread performance.
Intel does not depend on fast ram for performance.

 

[Ralston18]

Not sure about the context here.

In any case what motherboard is being considered?

The motherboard needs to support the installed (all of the installed) components.

Including CPU and RAM.