Ribbon cables: How much do you lose?

Hardware Hub GPU
1

So, here's a question. A ribbon cable for PCIe connecting a GPU to the motherboard. Let's assume it's PCIe, the cable is 6", and the card is a GTX 1080. If something as small as a lithography jump from 28 down to 16 can increase performance so much, how much does 6" inches of data travel hurt? Is there a lag because of the extension, or is it instant? If so, how bad is the performance drop?

2

Cable length and cpu lithography are unconnected

Cable will not make any noticable difference.

2 Likes
3

Well, that's good to know.

4

PCIe is a parallel bus. If you look at older pre-DDR4 motherboards, you'll notice that the traces leading straight to the RAM have lots of small wiggles in some of the traces. That's because the traces need to all be exactly the same length, because with parallel data transferral, all the data needs to arrive at the same time otherwise there will be latency issues all over the place.

PCIe is no different. All the contacts in the PCIe slots have the same length for each data pin leading to the controller or the CPU.

TL;DR, because PCIe is a parallel bus, as long as all the wires/traces on the riser cable are exactly the same length you should experience no performance hit at all, and if there is one, it will be down to latencies caused by a poorly manufactured riser cable. The riser cable just existing should not have any effect at all.

2 Likes
5

absolutely no difference
http://www.overclock.net/t/1427731/pci-express-extender-cables-benchmarked

the one I bought peforms exactly the same as in the slot, save for minutely more latency

1 Like
6

Nobody has mentioned yet, don't forget electrical interference. If you don't have a properly shielded ribbon you'll get more interference the longer it is technically... but that doesn't have to do with "performance" per se. If it picks up electrical noise my understanding is it just doesn't work.

7

That's why you don't buy the shitty ones on Amazon with the blue tape

Get the good 3M cable like I did

1 Like
8

Right, makin sure the OP knows that.

1 Like
9

I believe linus tech tips did a video on the max length of a PCIe extender ribbon..I think they got to like 6 ribbons before there was any noticeable drop in performance.

1 Like
10

That's amazing..