Noob questions about PCI-E lanes

[Lee Saxon]

I'm designing a system that will use a single video card (x16 obviously) and a RAID card (x4).

Many of the boards I've looked at, such as the Asus P7P55D-E Pro, offer two x16 slots but switch to x8/x8 when you utilize both.

How much of a damper am I going to put on my video card performance by limiting it to x8?

Also what are the 2.5GT/s or 5GT/s specifications listed next to many x1 slots?

Thanks

 

[ScorcherDarkly]

Going from x16 to x8 isn't a huge hit, but there is a hit (~5% if I remember correctly). Easiest way to find out the effect it might have on your hardware would be to look at benchmarks comparing SLi/CF in a 1366 board (x16/x16) to performance in an 1156 board (x8/x8).

If you're wanting x16 graphics and only x4 for your RAID card, get a mobo that has a dedicated x4 slot. Quite a few boards offer this now. For sure the eVGA p55 boards have them. Using this kind of board gets you around the problem completely.

A GT/s is one gigatransfer per second. Here's some reading: http://en.wikipedia.org/wiki/Transfer_(computing).

 

[happy medium]

A 5780 on a 8x pci-e 2.0 takes a 3% hit.

 

[cbn]

A 5780 on a 8x pci-e 2.0 takes a 3% hit.

How about a HD5970?

 

[vj8usa]

A 5780 on a 8x pci-e 2.0 takes a 3% hit.

Not even. Overall performance hit in techpowerup's article was 1-2%.
http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html

 

[Lee Saxon]

Sweet, thanks y'all.