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Comment by diffeomorphism | Hacker News Reader

Is shared ram any useful? For instance a mini PC with an AMD 7940HS chip and 64GB of ddr5 ram costs about 800€. At less than half the price of just a GPU, I am not expecting any great results, but is it usable?

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I was curious about this topic too because M3 macs have "Unified memory" which is shared amongst their CPU/GPUs. Anyone have a link or explanation of how this works?

One of the main bottlenecks for inference is memory bandwith (esp when dealing with huge models, like SD/SDXL) and for that, nothing I know of comes close to matching memory speeds on Apple Silicon (up to 400GB/s).

You can run very large models on a Macbook M2 with 96 GB. They run 1/3 to 1/4 slower in tokens/s than the faster hardware, but they fit in memory.

(400 GB/s is a lot in the form factor but the 4090 and equivalent have 1 TB/s, and H100s several times that)

Edit: Here someone asked the same question: https://www.reddit.com/r/LocalLLaMA/comments/14319ra/rtx_409...

Thanks, I've been trying to find this information - Mac shared memory vs Nvidia VRAM performance differences - for the longest time and your answer and the Reddit link were both super helpful!

You’re welcome — it’s too late for me to edit my wording but hopefully you understood what I meant by “1/3 to 1/4 slower.”

That is ambiguous, instead I should have said that models that fit in memory on both take 3-4 times as long on the M2 as they do on the 4090.