PCI-Express bandwidth and lanes, How do they all work?

[hcforde]

I have just learned that the x16 PCI-express slot has a bandwidth of 8GB/Sec. An x4 PCI express slot has a bandwidth of 2GB/sec the same as an 8x AGP slot, Yet my single x1900xtx has a bandwidth of over 50GB/sec. How does this work then that one card PCI express card is faster than another once you hit that 8GB/sec barrier. What am I not taking into account?

I know there are lanes which I believe I read somewhere run at 500MB/sec. That would mean that either the chipsets have increased the bandwidth either by increasing the number of lanes or increasing the capacity of current lanes. Do some motherboards have more lanes than others on the PCI-Express bus?

2 x16 slots + 2 x4 slots = total x40 slots = 40*500MB/sec = 10GB/sec on PCI-Express

Now, I have an Asus A8N-SLI motherboard if I put in a single card in it works at x16 If I put in 2 cards they work at x8 each. Does this still happen when using the cards as single cards (4 monitor outputs)and as an SLI setup? Does this bandwidth ever get saturated? I know that Gigabyte has a 4 PCI express motherboard the Quad Royal and Asus and others have boards that stay at x16 even with 2 cards loaded. but I just want to understand the basics of PCI-express and how it works first.

Is there a PCI-Express primer somewhere?

Is it possible to saturate the bus in using strictly 2D programs with say 6 monitors?

Thanks

 

[Pompeii]

As far as I know, there is simply no video card capable of saturating the pci-express bus, be it x8 or x16 slots.

Now, the 50gb/s bandwidth for the video card is most likely internal. Meaning the bandwidth between the gpu core and the gpu ram.

But keep this in mind, some other devices also run off of the pci-express bus. Such as the integrated lan and possibly the integrated sound, not to mention SATA ports.

I may be wrong with this stuff, not really my area. Feel free to correct me.

Here is a link explaining most of it:
http://en.wikipedia.org/wiki/PCI-Express

 

[cleeve]

Don't be overly concerned with the theoretical bandwidth numbers. In reality, even AGP 8x performs on par with PCIe 16x.

Bus bandwidth isn't the bottleneck.

 

[4745454b]

Pompeii was right, he just wasn't sure of himself. The 50gbps figure is the bandwith between the video cards processor and its memory. Motherboards currently only provide 16 lanes of PCIe to the slot. Don't worry about the gigibit networking, or other devices using PCIe. It isn't shared like old PCI. Each device has its own lane, and won't grab other devices bandwith. (you are limited to the total lanes provided by the motherboard.)

 

[sweetpants]

I have just learned that the x16 PCI-express slot has a bandwidth of 8GB/Sec. An x4 PCI express slot has a bandwidth of 2GB/sec the same as an 8x AGP slot, Yet my single x1900xtx has a bandwidth of over 50GB/sec.

I would imagine the 50GB/s is on the card PCB itself, rather than across the system board.

I don't know of any video cards (correct me if I'm wrong) that saturate the PCI-e bus.