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Ivy Bridge - PCI lanes basic question
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Br34ch
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Default Ivy Bridge - PCI lanes basic question - 04-09-2012, 10:33 | posts: 11 | Location: Brussels

I understand Ivy Bridge MBs have only 16 PCI lanes. I understand I can run 8x/8x 3.0 SLI. However, I have an external sound card (PCI-E 2.0 1.0) - hence my question - if I stuck this card in a 1x slot will this mean my second graphics card will be forced to 4x?

I'm looking at this MB:
http://www.asus.com/Motherboards/Int...specifications

And though it says:
2 x PCIe 3.0/2.0 x16 (x16 or dual x8) *2
1 x PCIe 2.0 x16 (x4 mode, black) *3
3 x PCIe 2.0 x1

I don't see how it can be dual x8 AND 4 more PCIe x1 - doesn't that translate into 20 lanes...? Thanks.
   
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Matt26LFC
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Default 04-09-2012, 12:18 | posts: 2,517 | Location: UK

I'm not sure, but I think one of your cards will be sent down to 4X because of your soundcard.

Its not the end of the world though as 4X PCI Gen3 is the same as 8X PCI Gen2. I belive the performance loss is like a couple %

However you would, I think, need a Gen3 supported graphics card for this to work.

Maybe a board with one of those PLX chips would help you if you upgrade.
   
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Default 04-09-2012, 13:04 | posts: 1,312 | Location: The Netherlands

It's the Ivy Bridge CPU that has only 16 PCIe 3.0 lanes available for the graphic card(s).
The Ivy Bridge chipset on that mobo will add extra PCIe 2.0 lanes: 1x x16 (@x4) + 3x (or 4x?) 1x.

SLI users are running Sandy Bridge with 2 PCIe 2.0 @x8 for graphics but can still add more PCIe devices such as sound cards. Ivy Bridge will support this as well.

Last edited by FatBoyNL; 04-09-2012 at 13:10.
   
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BLEH!
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Default 04-09-2012, 14:25 | posts: 4,961 | Location: London

Remember you do get 8 x PCIe 2.0 lanes from the Southbridge. Have a look in the manual to see which of the PCIe x1 lanes attach to, and stick it in the 2.0 lanes if you can.
   
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Br34ch
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Default 04-09-2012, 15:48 | posts: 11 | Location: Brussels

Thanks, this helps! Wish manufacturers would explain this in plain English to users on their web sites (I'm sure some do).
   
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Default 04-09-2012, 16:01 | posts: 3

On a related topic:
I'm thinking of upgrading my PC and getting 2x GTX680 in a 2-way SLI configuration.

What motherboard should i get ? Since the card supports PCI-e 3.0, i guess a Z77 is in order, but do i need to get one with a PLX chip to get 2x PCIe3.0 @ x16/x16 ? or can i get a cheaper one with 2x PCIe3.0 @ x8/x8 ?

What's the difference in performance between the 2, if any?

<3 in advance
   
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Br34ch
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Default 04-09-2012, 17:09 | posts: 11 | Location: Brussels

Quote:
Originally Posted by fbatista View Post
On a related topic:
I'm thinking of upgrading my PC and getting 2x GTX680 in a 2-way SLI configuration.

What motherboard should i get ? Since the card supports PCI-e 3.0, i guess a Z77 is in order, but do i need to get one with a PLX chip to get 2x PCIe3.0 @ x16/x16 ? or can i get a cheaper one with 2x PCIe3.0 @ x8/x8 ?

What's the difference in performance between the 2, if any?

<3 in advance
I'm not really an expert in this, but from what I've read so far:

a) You can't get PCI-e 3.0 x16/x16 on Z77 PLX or not - you need to go to X79
b) That said - no card in the foreseeable future will be able to saturate PCI-e 3.0 x16
c) Performance-wise PCI-e 3.0 x8 = PCI-e 2.0 x16 (provided you have a PCI-e 3.0 card of course)
d) Given that the real-world performance difference between PCI-e 2.0 x16 and x8 is about 1-2% the quest for PCI-e 3.0 x16 seems even less important.

I'm in the same boat as you - PCI-e 3.0 x8/x8 is plenty good for dual SLI IMHO.

Last edited by Br34ch; 04-09-2012 at 17:12.
   
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fbatista
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Default 04-09-2012, 17:27 | posts: 3

I said about the x16/x16 cause i've found 2 mobos that claim to support it:
- Gigabyte G1.Sniper 3 -> http://www.gigabyte.com/products/pro...px?pid=4169#sp
- ECS Z77H2-AX -> http://www.anandtech.com/show/5728/i...and-biostar/11

These 2 seem to have the PLX chip so that they support 3-way and quad sli. But, given these options, and since i dont want 3-way or quad SLI, but just 2-way... is it worth it ? :/

I' also think that pci-e 3.0 x8/x8 would be enough, but since all the benchmarks on the 680 2-way sli (that i found) are made on x79 or x58 boards (both support PCIe 2.0 x16/x16) i'm a bit scared :/ Mainly because i dont really want a board that doesnt use LGA 1155 socket, since i'm aiming to buy one of the new 22nm processors (i7 3770k or i5 3570k)...

Last edited by fbatista; 04-09-2012 at 17:30.
   
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Br34ch
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Default 04-09-2012, 17:30 | posts: 11 | Location: Brussels

Quote:
Originally Posted by fbatista View Post
I said about the x16/x16 cause i've found 2 mobos that claim to support it:
- Gigabyte G1.Sniper 3 -> http://www.gigabyte.com/products/pro...px?pid=4169#sp
- ECS Z77H2-AX -> http://www.anandtech.com/show/5728/i...and-biostar/11

These 2 seem to have the PLX chip so that they support 3-way and quad sli. But, given these options, and since i dont want 3-way or quad SLI, but just 2-way... is it worth it ? :/
OK, I stand corrected ;-) I'd say no, not worth it given the bandwidth PCI-e 3.0 demand/supply and GPU evolution, but perhaps I'm wrong. As I said PCI-e 2.0 x16/x16 = PCI-e 3.0 x8/x8 - the question is whether PCI-e 3.0 x16/x16 will result in any tangible difference, but I very, very much doubt it'll be over 1%. Cheers.
   
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fbatista
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Default 04-09-2012, 17:36 | posts: 3

I found a benchmark on an ATI 7970 card comparing different PCIe 3.0 speeds:

http://www.anandtech.com/show/5458/t...cking-and-msaa

Seems really on the spot of what we were saying here
   
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sykozis
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Default 04-10-2012, 00:13 | posts: 16,766 | Location: US East Coast

Quote:
Originally Posted by Br34ch View Post
I'm not really an expert in this, but from what I've read so far:

a) You can't get PCI-e 3.0 x16/x16 on Z77 PLX or not - you need to go to X79
b) That said - no card in the foreseeable future will be able to saturate PCI-e 3.0 x16
c) Performance-wise PCI-e 3.0 x8 = PCI-e 2.0 x16 (provided you have a PCI-e 3.0 card of course)
d) Given that the real-world performance difference between PCI-e 2.0 x16 and x8 is about 1-2% the quest for PCI-e 3.0 x16 seems even less important.

I'm in the same boat as you - PCI-e 3.0 x8/x8 is plenty good for dual SLI IMHO.
You can get x16 SLI on a motherboard with a PLX chip as it can "broadcast" just like the NF200 chip does....just depends on which chip the board has.
   
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slickric21
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Default 04-12-2012, 13:44 | posts: 2,137 | Location: U.K

Dont those PLX chips, like the NF200 does iirc add extra latency though that negates their effectiveness in some way ?
   
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