PCIe Slot Confusion

[BossBruce1]

Could anybody explain PCIe slots to me? I do not understand which slots correspond to 8x, 16x, 4x, etc. Is there a visual way to tell? And also what slots would you put two graphics cards in SLI on an Asus X99 Deluxe Motherboard if the number of lanes I had was sufficient? Thanks. (sorry I'm new to PC building >_<)

 

[derekullo]

https://en.wikipedia.org/wiki/PCI_Express

Has a nice graphic showing different sizes x1, x4, x16

https://upload.wikimedia.org/wikipedia/commons/f/fc/PCIExpress.jpg

As you can see x16 is physically the biggest since it has 16 lanes.

Each lane consists of 4 wires, so a pci-e x16 would have 64 wires

 

[derekullo]

Taking a look at that motherboard it appears all of your pci-e are x16, except for a lone x4 which as you may have seen is about 1/4 the size of the other 5.

40-Lane CPU-
5 x PCIe 3.0/2.0 x16 (x16, x16/x16, x16/x16/x8, x8/x8/x16/x8, x8/x8/x8/x8/x8 mode)

28-Lane CPU-
3 x PCIe 3.0/2.0 x16 (x16, x16/x8, x8/x8/x8)
2 x PCIe 2.0 x16 (x1 mode)

The lanes available for use on each x16 slot is dependant on the processor.

For the most part it doesn't really matter even if you had a 28 lane cpu.

There is little difference between running a card at x8 or x16.

http://www.tomshardware.com/reviews/graphics-performance-myths-debunked,3739-3.html

 

[derekullo]

In conclusion, if you need to use an sli bridge then make sure the graphics cards are close enough for it to reach.

If it does not require one then put some space between them, put one in slot 1 and another in slot 4, for instance.