Gigabyte P55 UD4 - PCI Express Question

[gjn]

This board has two PCIE 2.0 slots, one labeled x16 and the other x8.

I've got a zalman cnps 10 installed and it nearly covers the top PCIE slot, and for the sake of comfort I would like to install my video card in the lower slot (marked x8).

The specs on newegg state there are two x16 slots so i'm thinking it doesn't matter which one I use in a single card setup, but the Gigabyte manual "recommends" using the top slot.

Does it matter which? Will there be a degradation in performance using the lower?

Should I just use the top slot (with an 1/8th inch of clearance between the heatsink and the back of the card)?

Thanks for any suggestions...

Cheers,
gjn

 

[lopri]

Hello and welcome to AnandTech Forums. Check out the old sticky thread linked below.

http://forums.anandtech.com/showthread.php?t=286944

 

[gjn]

Hey Thanks lopri.

Based on this from the sticky:

PCI Express 2.0 (PCIe Gen 2)

x1 = 0.5 GB/s (1.0 GB/s duplex)
x4 = 2.0 GB/s (4.0 GB/s duplex)
x8 = 4.0 GB/s (8.0 GB/s duplex)
x16 = 8.0 GB/s (16.0 GB/s duplex)

I suppose yes there will be a performance degradation if I use the x8 slot and leave the x16 open.

Would this be a good assumption?

 

[lopri]

There may be performance loss incurred depending on applications, yes. But I wouldn't say it's prohibitive. In that sticky thread, I had linked to an AnandTech article which investigated the question you have.

http://anandtech.com/mb/showdoc.aspx?i=3649

We are also reporting single card results with the HD 5870 running at PCIe 2.0 x8 speeds on the P55 platform to compare performance to the x16 single card setup. We installed an Intel CT Gigabit network card in the second physical x16 slot in order to force x8 operation.

So it looks like some games do take performance hit, at least with an HD 5870. Having said that, I have used GT200/RV770 class cards on x8 bandwidth without any perceived difference in the past.

 

[gjn]

Ok, thanks for clarifying. See what happens when you read posts when ur half asleep

I'm actually using a 5770, but upgrading from system with a 9700 pro (yeah i know). So even if there is a difference I would most likely have no clue.

My biggest concern is the cards proximity to my CPU Cooler. I can mount everything just fine, but the back/top of the card is literally a 16th of an inch from the Cooler.

Should I be worried about anything?

Thanks again for your insight.

 

[lopri]

Concentrated heat on upper-left side of a motherboard can be a concern for a long term, yes. But having said that, P55 system is extremely cool running system compared to previous Intel's offerings. It doesn't have north bridge on board, and according to AT reviews the mosfets are ridiculously cool. (like ~60C max)

When I ran a 4890 on the 2nd x16 slot (x8 bandwidth), I didn't lose any performance - that is, until I enabled Cool'n Quiet. For whatever reason, when I enabled C'nQ, I experienced weird performance issues like frame skipping. It was doubly weird because such issues didn't occur with all games. Only a select few games showed such behaviors. Installing the video card on the first x16 slot or disabling C'nQ solved it.

So I think there is no definite answer, unfortunately. Theoretically the only disadvantage of 2nd x16 slot should be physical distance (i.e. latency) to the PCIe controller, but some boards handle things better and some worse, so I suggest you test it out yourself. Thankfully moving around video card shouldn't be too difficult.