How much performance increase from PCIe 1.0/1 to PCIe 2.0?

[Pentacore]

My motherboard only supports PCIe 1.1. I'm running 2 8800GTs in SLI however both cards support PCIe 2.0. So my question is if I bought a new mobo that supports PCIe 2.0 and put these same cards in, how much of a performance increase would I see? Would it be worth buying a new motherboard? As I understand it, SLI in PCIe 1.1 has both slots running at only 8x mode where if I had a mobo with PCIe 2.0 both slots would be running at 16x mode? Is that right?

Thanks in advance!

 

[Team42]

AnandTech Discourse on PCIe 2.0

tomshardware benchmark

It would appear that PCIe 2.0, while a very good idea, is still in it's infancy.

The difference between 2 cards running at 8x and 16x in Crossfire is, to most people, imperceptible at the moment.

That said, it is the way forward, given the significant bandwidth improvementso over PCIe 1.1.

P45 chipsets only support 2 PCIe 2.0 slots in 8x mode (1 in 16x mode). X38 and X48 both support 2 slots in 16x mode.

You pays your money, you picks your mobo...

T42

 

[taltamir]

please note that they tested two 3850, this is a pretty old article. Tests have shown that last gen cards like the 3850 loose a good amount of performance while in SLI / CF with less then the full 16x of PCIe 1. But not a significant amount with pcie 1 vs 2...
But the amount of bandwidth needed increases as the speed of the parts increase. However, he does have a pair of 8800GT, not newer cards like the G200 or the R770.

Originally posted by: Pentacore
As I understand it, SLI in PCIe 1.1 has both slots running at only 8x mode where if I had a mobo with PCIe 2.0 both slots would be running at 16x mode? Is that right?

No that is not correct.
PCIe 2 is twice as fast as v1. And the split of lanes has nothing to do with the version.
Some motherboards are v1 with 8x/8x split. some are v1 with 16x/4x (or was it 8/4?), some are v1 with 16x/16x, some are v2 with 16x/16x, some are v2 with 8x/8x...

v2 is twice as fast per lane then v1. So 8x v2 = 16x v1. 16x v2 = 32x v1.
The 16/4 (or was it 8/4?) is the absolute worst performer, significant reduction even with your setup. as far as I remember, 8x/8x v1 is about 10% slower I think then 16x/16x v1 (8x/8x v2).

Anyways, regardless, I wouldn't bother upgrading your mobo to a faster SLI standard right now. your performance will probably improve too little to justify such an upgrade.

 

[Team42]

Originally posted by: taltamir
please note that they tested two 3850, this is a pretty old article. Tests have shown that last gen cards like the 3850 loose a good amount of performance while in SLI / CF with less then the full 16x of PCIe 1. But not a significant amount with pcie 1 vs 2...
But the amount of bandwidth needed increases as the speed of the parts increase. However, he does have a pair of 8800GT, not newer cards like the G200 or the R770.

Originally posted by: Pentacore
As I understand it, SLI in PCIe 1.1 has both slots running at only 8x mode where if I had a mobo with PCIe 2.0 both slots would be running at 16x mode? Is that right?

No that is not correct.
PCIe 2 is twice as fast as v1. And the split of lanes has nothing to do with the version.
Some motherboards are v1 with 8x/8x split. some are v1 with 16x/4x (or was it 8/4?), some are v1 with 16x/16x, some are v2 with 16x/16x, some are v2 with 8x/8x...

v2 is twice as fast per lane then v1. So 8x v2 = 16x v1. 16x v2 = 32x v1.
The 16/4 (or was it 8/4?) is the absolute worst performer, significant reduction even with your setup. as far as I remember, 8x/8x v1 is about 10% slower I think then 16x/16x v1 (8x/8x v2).

Anyways, regardless, I wouldn't bother upgrading your mobo to a faster SLI standard right now. your performance will probably improve too little to justify such an upgrade.

Yeah, cheers, that was so much clearer than what I said.

A handy ready reckoner

T42

 

[Pentacore]

Thanks all for the info. My mobo is the ASUS P5N-E SLI that does 8x/8x so I just keep it for a while. Thanks!