Double PCI express gen3 Video Cards with I7 processor

Gianluca Lamanna · May 30, 2013

Dear all,
I would like to install two Video Cards NVIDIA TITAN on the same PC. The main purpose will be scientific computing and I need to full exploit the pci gen3 X16 bandwidth. Apparently the number of pci lines to the I7 processor isn't enough to support two cards. My trivial question is (I'm sorry I'm not an expert): in which way motherboards (like the asrock Z77 extreme 9) designed for I7 or E3, can support two X16 boards (from the specs of this board it's written that it's possibile to have two X16 at the same time)?
Thanks for yours answers,
g.

Ohmybad · May 30, 2013

you want the LGA2011 socket, X79 it has more the support for 2+ 16x pcie.

Someone Somewhere · May 30, 2013

I highly doubt that PCIe3.0x8 per card isn't enough for whichever scientific computing you are talking about - that's about 8GB (not Gb) per second in each direction. Equivalent to PCIe 2.0x16.

They share the lanes between the two cards, so each runs at x8 if you have two.

Gianluca Lamanna · May 30, 2013

Ohmybad :

I see. But, still, I can't understand why in the specs of the Z77 it's written that the board support two X16 (it's not specified that they are downgrade to X8): is it something related to the sli connection?

Gianluca Lamanna · May 30, 2013

Someone Somewhere :

Thanks for your answer. In high energy physics application the quantity of data is very huge indeed (in some case (not on single PC of course) several TB/s).

Someone Somewhere · May 30, 2013

Yes, but the GPU itself can't deal with the data as fast as it's given it usually. For example, most compute applications, things like Folding etc. and hashing can use a single lane, and not saturate it.

They have two slots that can physically fit 16-lane cards, but one of them is only wired for x8, and steals those lanes from the first slot when in use.

Gianluca Lamanna · May 30, 2013

Someone Somewhere :

our application is very peculiar: the algorithms it self is so easy (and fast) that the limitation is, in any case, the data transfer. We like the GPU because we can parallelize the processing of different "events" on the multiprocessors more than the parallelizaztion of the code.

If I understand correctly (but, I'm sorry again I'm not a big expert) in the Z77 extreme9 there are 5 connectors that mechanically can fit 16-lanes cards. What is written on the specs is that it allow to use at X16 two boards in special position. it's written:
- 5 x PCI Express 3.0 x16 slots (PCIE2: x16 mode or PCIE1/PCIE3/PCIE5/PCIE7: x16/0/16/0 or x8/8/8/8 mode)
This is puzzling me.
g.

Someone Somewhere · May 31, 2013

Oh - very high end boards with a PLX-something chip can mirror the data from the CPU to two different GPUs, because SLI/CF configs need the same data to go to both GPUs. It won't work if you intend the GPUs to work with different data.

Where is this data coming from - there's no way to get 16GB/s into the system, except out of RAM or CPU Cache. Sounds like you need to compress stuff.

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