PCI-E riser - what are maximum lengths?

T

tankman1989

Gawd
Joined
Aug 21, 2009
Messages
588
I need to find out what the maximum length would be for a PCI-E riser for at least a x1 slot but ideally a x16. I have seen systems where an external box with something like a motherboard (daughterboard??) was connected to add more video cards. The cable was pretty long, maybe almost 2 meters, but IDK if that was just the way it looked on the image.

Any idea of useable lengths?
 
Someone over at overclock.net tested several lengths of PCIe riser cables a while back. Here is his conclusion:

Based these benchmark results, I conclude that there is no measurable performance impacts when using PCI express extenders compared to in-slot configuration. In addition, there is no measurable performance impacts between different types and lengths of extenders used.
Click to expand...

The thread can be found here.

The lengths tested were well under several meters however. It looks like he tested a maximum length of 500mm (0.5m) worth of riser cable. The tests were also done on an older 5870. I know a lot of miners were using riser cables to squeeze more cards per box and as far as I had read, it worked fine. I don't think crytocurrency mining actually stresses the PCIe bus, if I recall correctly.
 
Thanks for the links. I had seen the one on OC.net but the thing is that the results showed almost no difference between the cables and there was no testing of any cable that seemed to fail because of length. I found that there wasn't any defined max length for extension cables and there hasn't been any defined cable max for external PCI-E cabling either.

As for the second poster, the max length listed is under what some other posts and products I have found make claims to support, so IDK where it stands.

I'm wondering how much the cable length limitation is a result of power transmission over the riser cable. If the external device connected to the riser had its' own power supply to the slot, would that allow for a longer cable. This is especially critical for the 3.3v pins (there are 4 of them) as these will have the most significant voltage decrease over the riser configuration.

seems like this may be a nice little DIY test project :)

Also, if 2 systems were connected with a slot to slot connection (x1, x4, x8 or x16, any of these), what would they be able to do and would that even work??
 
The biggest issue with PCI-e extenders is not going to be length per say. It is going to be interference with other electronics in proximity.
 
tankman1989 said:
I need to find out what the maximum length would be for a PCI-E riser for at least a x1 slot but ideally a x16. I have seen systems where an external box with something like a motherboard (daughterboard??) was connected to add more video cards. The cable was pretty long, maybe almost 2 meters, but IDK if that was just the way it looked on the image.

Any idea of useable lengths?
Click to expand...

Apparently these can go up to 2 meters without loss http://www.amazon.com/dp/B07997Q5L7
& these up to 4.5 meters http://www.amazon.com/dp/B07B9KQSDX
 
As an Amazon Associate, HardForum may earn from qualifying purchases.
You must log in or register to reply here.
Back
Top