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Noob questions about PCI-E lanes

Lee Saxon

Jan 31, 2010
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?



Senior member
Aug 7, 2009
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).