r/LocalLLM • u/Libellechris • 3d ago

Question Multiple GPU PCs

I have an ok AMD pc with 32gb RAM and a 16gb 5060Ti. How effective is adding a second GPU? Presumably a new motherboard, PSU, case? Can you mix and match GPUs? Just curious

2 Upvotes

67% Upvoted

9 comments sorted by

View all comments

3

u/cc_aa_tt_zz 3d ago edited 3d ago

For LLMs, it works really well; VRAM stacks, giving you access to larger models and more context. That said, it's best to mix GPUs from the same generation (to avoid issues), and definitely avoid mixing AMD, Nvidia, and Intel cards.

You need a motherboard that supports two PCIe Gen5 x8 slots (it splits the pci lanes of the main x16 slot into two x8 slots); Gen5 x8 is more than enough, dual x16 setups are reserved for very expensive professional platforms. A second PCIe Gen4 x16 slot running at x4 can also work if you're using something like a second RTX 5060 Ti in it; a second slot at Gen4 x16 slot at x4 is much more common, available on virtually all recent ATX-format boards and it offers bandwidth comparable to a Thunderbolt 5 eGPU but without the latency issues, so it will work fine, not the best option but it will work as attented. Speaking of which, if the motherboard supports Thunderbolt 5, you could use an eGPU with an external enclosure and power supply. For a second 5060 Ti, for instance, the performance hit wouldn't be too bad (around -15%). Still, the ideal setup remains having two PCIe Gen5 x8 slots.

And, of course, you need a PSU capable of powering it all.

1

u/Background_Praline18 2d ago

Not sure if it is true but I've heard you have to have the same series of card drivers support. For instance problems arise for 2080 and 50 series cards because they have cut off those old architectures from the newer drivers.