290X Number Of PCI-E Lanes ?

Dicehunter · 15 Jan 2015 at 15:19

Anyone by chance know how many PCI-E lanes the 290X uses ? As in the number of lanes a CPU has etc...Just curious as to how this works

VincentHanna · 15 Jan 2015 at 15:27

On the CPU you have (Devils Canyon) you have 16 CPU lanes.

With one device plugged it, it'll get the full 16 lanes.

Anymore than that and it'll have to share lanes. Presumably 8/8

A Haswell-E 5820 CPU has 28 lanes and the Haswell-E 5930k and 5860x have 40 CPU lanes, so are considered better for people with 3x GPU's or more.

shankly1985 · 15 Jan 2015 at 15:29

You can also get PLX Motherboards that controls the PCI lanes.. Like my ASUS p8 z77 WS does 32 lanes I think dual 16x

Orangey · 15 Jan 2015 at 15:32

Could be wrong but I'm pretty sure a GPU would use however many lanes you gave it. Although strangely it wouldn't make a difference past a certain point.

Tonester0011 · 15 Jan 2015 at 15:35

Normally 16x 1 card
8/8 for two or 8/4/4 for three plx boards to enable more than two card Nvidia etc.

Dicehunter · 15 Jan 2015 at 15:50

Thanks fore the replies peeps, so out of curiosity how many lanes would a 290X need to operate efficiently ?

VincentHanna · 15 Jan 2015 at 15:52

In PCIE 3.0? 8

There's not much difference between 8 and 16.

Dicehunter · 15 Jan 2015 at 15:54

Cooleo well that sorts that out then, Thanks peeps

shankly1985 · 15 Jan 2015 at 15:55

Dicehunter said:
Thanks fore the replies peeps, so out of curiosity how many lanes would a 290X need to operate efficiently ?

It would be 16x, and as low as 4x

mmj_uk · 15 Jan 2015 at 15:59

What it boils down to is bandwidth.

1x PCI-E 2.x lane = 500 MB/s
1x PCI-E 3.0 lane = 985 MB/s

4790K has a total of 16 PCI-E 3.0 lanes.

8x PCI-E 3.0 lanes is roughly equivalent to 16x PCI-E 2.x lanes.

Those PLX switches that shankly1985 mentioned just kind of emulate extra lanes, the connection between the PLX chip and CPU is still the same bandwidth.

shankly1985 · 15 Jan 2015 at 16:02

But do get better performance with pci 3.0 16x and 8x vs my other none plx board 8x8x

The pci 3.0 is a strange one, GPUz reports am running 3.0

humbug · 15 Jan 2015 at 16:32

I have had mine running in the PCIe2 8x, there is about a 3 to 5% performance drop compared with 16x

pandem0nium · 15 Jan 2015 at 16:47

shankly1985 said:
The pci 3.0 is a strange one, GPUz reports am running 3.0

Yeah, just ignore that. You have to use it's rendering test tool thing before it'll tell you what it's actually running as.

shankly1985 · 15 Jan 2015 at 17:38

pandem0nium said:
Yeah, just ignore that. You have to use it's rendering test tool thing before it'll tell you what it's actually running as.

Yeah that's what I do lol but it still says am running pci 3.0

drunkenmaster · 15 Jan 2015 at 18:21

mmj_uk said:
What it boils down to is bandwidth.

1x PCI-E 2.x lane = 500 MB/s
1x PCI-E 3.0 lane = 985 MB/s

4790K has a total of 16 PCI-E 3.0 lanes.

8x PCI-E 3.0 lanes is roughly equivalent to 16x PCI-E 2.x lanes.

Those PLX switches that shankly1985 mentioned just kind of emulate extra lanes, the connection between the PLX chip and CPU is still the same bandwidth.

Strictly speaking they don't, they have more. The cpu has a direct 16x pci-e 3 connection but the cpu also has a high bandwidth connection to the southbridge chip which also has up to 8 pci-e 2.0 x1 slots with more bandwidth available.

I presume on a PLX based board where as the pci-e 3 on the chipset is usually connected directly to the slots and NOT through a chip, the PLX chip is connected to the pci-e slots, then the plx chip is connected both through the normal 16x direct to cpu connection AND using some of that bandwidth through the chipset, doing some fancy balancing of load stuff I would presume.

SO there is say 16GB/s of bandwidth direct to the CPU and 5GB/s through the chipset, with the PLX chip you can connect these together before going to the pci-e slots.

EDIT:- DMI 2.0 seems to be a 20Gbit/s speed, so about 2.5GB/s of which you'd say the majority actually during a game/benchmark(after it's loaded and hd access is minimal) would be available, so a 15% or so increase over the solo 16x slot.

EDIT2:- more reading, the plx chip also creates lots of extra pci-e lanes because a decent amount of traffic is just from one gpu to the other, not back to the CPU. So by adding extra lanes the gpu's can talk to each other without eating up the bandwidth available from the cpu. I could see both methods improving performance tbh. Why Intel doesn't have a "gaming" chipset which adds this to a southbridge naturally I really don't know.

shankly1985 · 15 Jan 2015 at 18:29

So the real question is am I really running pci 3.0 with sandy or is GPUz drunk?

Orangey · 15 Jan 2015 at 18:49

This is my go-to link on PLX multiplexing.

http://www.anandtech.com/show/6170/...x-8747-featuring-gigabyte-asrock-ecs-and-evga

mmj_uk · 15 Jan 2015 at 18:52

I've not been able to find any diagrams showing it coupled to the DMI 2.0 link? I would think they'd want to separate Southbridge functions (SATA) from GPU traffic particularly as the PLX switches have been found to cause latency which can be a killer with sound cards etc.

Uncle Petey · 15 Jan 2015 at 18:55

shankly1985 said:
So the real question is am I really running pci 3.0 with sandy or is GPUz drunk?

Mine did the same thing with plx/sandy i7 lol. I just shrugged and carried on.

shankly1985 · 15 Jan 2015 at 18:57

mmj_uk said:
I've not been able to find any diagrams showing it coupled to the DMI 2.0 link? I would think they'd want to separate Southbridge functions (SATA) from GPU traffic particularly as the PLX switches have been found to cause latency which can be a killer with sound cards etc.

That was something I was reading up about before picking this board and was a gamble on my half.

So far I have used two sound cards, crossfire, single gpu and I have noticed no latency at all.
I also believe the plx is much improved upon since its launch.