Multiple GPUs for CUDA but not SLI Hardware requirement

I currently have an old GPU card 8800GTX in my system. If I add one more card to the system for accelerating computation,

  1. Do I have to switch my current system to a motherboard and system which SLI supports? Or SLI is irrelevant to multiple GPUs for CUDA?

  2. I have only one PCI-E x16 slot now, can I use a extender card to parallel the two cards? Will it harm the performance a lot? Or I have to use a motherboard with at least two PCI-E x16 slots?

Since the current information about multiple GPUs inside a system are targeting around SLI, I am a little bit confused if GPUs for computation have to follow SLI’s specification or not. Thanks for any suggestions.

Hi, you do not need an SLI system in order to run cuda on multiple devices.

In relation to the pci-e performance the theoretical throughput of pci-e x16 is 8000 MByte/s
for x8 it is 4000 MB for x4 2000 and so on…
(practical throughput however is lower; guess when getting 80% of the theoretical throughput you’re a lucky man )

If you have to transfer lots of data and do this really often than you should think about getting
a new motherboard that provides two x16 slots. if you only need to transfer data for the initialization of
your application and after that only transfer little data to get the result, it should not make any difference
for the overall performance if using x16 or x8.
There are some comparison tests out there for x16 and x8 performance (just google for it) but they mainly test
game performance there. So it hardly depends on the kind of application you are running…


Hi Tobi

Really appreciate your help. :thanks:

Hi Guys, I have somewhat almost the same situation here…I am setting my Mac Pro Version 3.1 (Dual core 2.8Ghz late 2008 model) to be my editing, color grading, and gaming system. Now I would like install my quadro 4000 and my Black Magic Design HD DeckLink card in my Mac and have GTX 285(for gaming) in my GPU xpander made by CUBIX ( along my Raid controller card. Now my question will this lower my bandwith or will this set-up is able to work?