PCIe x4 graphics bottleneck

[brshoemak]

I have an older machine (Intel Q6600/8GB) that only has a PCIe x4 slot for a graphics card - electrically limited, not physically limited. I am not looking for much out of this system given its ancient age, I just want to be able to run Bioshock Infinite at a decent framerates and high or ultra quality at 720p or maybe even 1080p (would be nice but not necessary).

How badly will this x4 limitation affect performance? Does anyone know the graphics chipset at which the x4 bandwidth would be the limiting factor instead of the GPU? It's currently rockin' a Radeon 4350 which holds its own for some games, but would likely choke on Bioshock.

 

[toyota]

lol a 4350 did not even hold its own on the day it came out. x4 on a pci-e 1.0 will probably take quite a hit. I would not bother with anything faster than a 7750 for sure as even that will be choked.

 

[brshoemak]

Hey I said "some" games - I never said 3D games. Mark of the Ninja runs like a dream on it.

The 7750 would clock in around $100 which is around what I was looking to spend. It looks like it comes in a couple fanless configurations which would be great so my wife won't complain (as much).

Is there a decent NVIDIA equivalent in that range or is Radeon the way to go for that generation?

 

[lopri]

It really depends on how the board implemented PCIe. And Q6600 runs on an old configuration where PCIe lanes can be running off of either north bridge or south bridge. If the slot is connected to the north bridge and is relatively close to the CPU socket, then performance loss should be minimum. But if the PCIe lanes go through the south bridge, then the performance penalty will be huge.

 

[Arkaign]

I don't think I'd advise spending more than say a used 6670 unless you're going to later move the card to a faster system. A 6670 is 1,000,000,000x faster than a 4350

 

[Arkaign]

Relevant : http://forums.anandtech.com/showthread.php?t=2200539

* note that PCI Express 2.0 X1 is actually slower than PCI Express 1.0/1.1 X4. So the bottlenecking is there, but not so overwhelming as to make a faster card useless.

 

[BigChickenJim]

I remember reading a while back that performance loss between x16 and x8 slots was around 3-5%. If that's true then you could reasonably expect to see a 6-10% loss on a x4 slot. If you consider that 1.0 PCI-E slots are more inefficient than 2.0 or 3.0 slots, I think you'd lose around 15-25% performance all told. Bear in mind that those numbers are extremely rough estimates and may be entirely wrong. Regardless of specific numbers, though, I think you're going to wind up in a situation where performance gains over your old hardware will struggle to exceed the bottleneck drop on the new card. I know you don't want to hear this, but it may be time for a new build, especially if you're looking to play modern games (even less intensive games like Infinite).

I'll see if I can dig up that article... Like I said, I could be entirely wrong. Just my two cents.

Edit: Found it. http://www.tomshardware.com/reviews/pcie-geforce-gtx-480-x16-x8-x4,2696-9.html

Looks like it's an 8% drop from x16 to x8, and a couple of their bench tests measured up to 50% loss (worst-case scenario) on the x4 slot. Granted, these numbers are from Nvidia cards, are at different resolutions, and were sometimes calculated while using Sli, so a grain of salt is in order. Still, those numbers are concerning. You'll need to see a pretty big performance leap to cover the loss and net a gain, and I'm not sure that'll come easily. Hope this helps.

 

[toyota]

it does not always work like that. going from 16 to 8 is not the same as going from 8 to 4.

 

[BigChickenJim]

it does not always work like that. going from 16 to 8 is not the same as going from 8 to 4.

Like I said, rough estimates. The math is obviously more complicated than a 1-to-X ratio and I'm only a nerd, not a math prof. My point is that I don't think it's worth it to invest in a new card. He's better off saving for an entirely new build.

 

[brshoemak]

@lopri - I have no idea if the PCIe lanes are off the northbridge or southbridge. It's a Dell SC440 but I'm not finding much on the architecture.

@BigChickenJim - Thanks for all the information, there's a lot to digest there. Also, I'm not enough of a gamer (anymore) to build a gaming rig. I have an ESXi server to build next and that will take a good chunk of change - and obviously won't work for gaming. If I can spend $50-$100 for a card that can play Bioshock and maybe some other older games and put it in my current machine that would be ideal.

Thanks for all the insights, I have some thinking to do. Worst case scenario I can try it and see what happens - just wondered what I might be in for.

 

[BigChickenJim]

The old try-and-see approach is still a perfectly valid course of action. I wish you luck; BioShock Infinite is an excellent game.

 

[Jimzz]

Make sure if you get a 7750 it has GDDR5, not DDR3.

But look for a 7770 or 7790 card with a rebate if you are in the $100 range.


What motherboard do you have?

 

[brshoemak]

The motherboard is from a Dell SC440 and I believe it uses the Intel E7320 chipset.

Here is a link to the architecture in case you want one.

That page shows a x8 slot which seems to be directly into the northbridge - but that is currently occupied by a SAS6ir card. The remaining PCIe slots seems to be handled by the southbridge, which seems odd to me.

 

[Jimzz]

^

Are you really using PCIe 8x bandwidth on the SAS6ir card? If not move it to the 4x and put the video card in the 8x.

But seems there are a lot of rebates and deals on the 7770 and 7790 cards now that make the 7750 more costly for the performance it offers.

 

[jacktesterson]

7770/7790 would work fine on that system.

 

[brshoemak]

^

Are you really using PCIe 8x bandwidth on the SAS6ir card? If not move it to the 4x and put the video card in the 8x.

But seems there are a lot of rebates and deals on the 7770 and 7790 cards now that make the 7750 more costly for the performance it offers.

The BIOS of this Dell board makes it so the x8 slot runs at x1 - no joke (although I wish it was) and has been confirmed on a couple sites. The x4 slot works at it's rated speed, so that's where the current video card resides.