CPU Multiple PCIe Riser Cards in Series

Brian McGuigan

Cable Smoosher
Original poster
Sep 17, 2022
10
7
Has anyone tried it? Did it work?

I am about to build my first SFF Case, for an 'Air-Cooled, Micro Workstation-Server', that I want to fit in my briefcase. Because of height restrictions, there is no space in the case for a full-sized GPU. But there is space in the case for a DIY eGPU.

So, what I would like to do is extend the PCIe Slot outside the case. (I am well aware about the USB 4, Thunderbolt 4, and Oculink options. So, don't bother to tell me about them.) What I want to do is physically extend the PCIe Slot to the outside of the case. Again, I realise I could use a PCIe Riser Cable, take through a slot and plug it into the PCIe Slot on the motherboard. But to do so, I'd have to open the case. NO, what I want to do is plug a Riser Cable into a PCIe Slot, situated in the open-air on the side of the case.

My idea is to plug a short Right-angled Riser Card into the PCIe Slot on the motherboard. I'd then plug a short straight Riser Card into that, which would take it out through the side of the Case. The second card would be screwed down, so that it would not move - even if the case cover was removed.

I know physically, it can be done, as I've already designed the case. The question is, will the PCIe signal degrade too much to be practical. So if you've already done it, please let me know.

The only reference I've found to anything similar, is a LTT video on YouTube, where they used multiple PCIe 3.0 Riser Cables in series - just to see if it could be done. They got out to 3.6M, before it stopped working! BUT, that was PCIe 3.0. I hope I can get away with two short PCIe 4.0 Riser Carsds, and a 20cm/8in, Riser Cable.
 

hrh_ginsterbusch

King of Cable Management
Silver Supporter
Nov 18, 2021
702
274
wp-devil.com
In theory, if the MB supports bifurcation, one could do that.

Also, there are "normal cable" like riser cables, eg. for mining or server builds. Got myself one of these for future builds. Cant really use it in the A4-H2O, but would be great for a console-like build, eg. my WIP sleeper.

On that topic: I've actually pondered about a similar concept to this about a year ago; the idea was to move MB + cooling to one case (5 L Chieftec Compact IX-06B) and the PSU + GPU to a second one. Later on, I came up with using one GaN 250 for the first and a second Gan 250 in the second case, only connection remaining the riser cable.

Never implemented it, but prep work etc. was already quite advanced.

cu, w0lf.
 

Brian McGuigan

Cable Smoosher
Original poster
Sep 17, 2022
10
7
In theory, if the MB supports bifurcation, one could do that.

Also, there are "normal cable" like riser cables, eg. for mining or server builds. Got myself one of these for future builds. Cant really use it in the A4-H2O, but would be great for a console-like build, eg. my WIP sleeper.

On that topic: I've actually pondered about a similar concept to this about a year ago; the idea was to move MB + cooling to one case (5 L Chieftec Compact IX-06B) and the PSU + GPU to a second one. Later on, I came up with using one GaN 250 for the first and a second Gan 250 in the second case, only connection remaining the riser cable.

Never implemented it, but prep work etc. was already quite advanced.

cu, w0lf.
I don't actually think it needs bifurcation. THat's needed if you want to split the lanes between cards. In my idea all lanes go through both cards, in series. So bifurcation will not be needed. The only issue is signal degradation going through two extra lots of cables. I've sounded out my supplier to see whether they'll let me try it out on a 'Sale-or-Return' basis. You idea of splitting the PSU + GPU off into a second case, is exactly what I'm proposing.

The only reason I haven't got my build proposal up yet, is that I haven't yet figured out how to upload pictures to ssf.Network. It looks like I've got to upload it to somewhere, like Dropbox, and then specify a link.
 

hrh_ginsterbusch

King of Cable Management
Silver Supporter
Nov 18, 2021
702
274
wp-devil.com
I don't actually think it needs bifurcation. THat's needed if you want to split the lanes between cards. In my idea all lanes go through both cards, in series. So bifurcation will not be needed. The only issue is signal degradation going through two extra lots of cables. I've sounded out my supplier to see whether they'll let me try it out on a 'Sale-or-Return' basis. You idea of splitting the PSU + GPU off into a second case, is exactly what I'm proposing.
Havent ever tried that.. despite my "out-of-the-norm" mods :)


The only reason I haven't got my build proposal up yet, is that I haven't yet figured out how to upload pictures to ssf.Network. It looks like I've got to upload it to somewhere, like Dropbox, and then specify a link.
yeah, that.

you get those rights if you're a supporter. I do understand that, the impact on SFF.net is probably pretty high - all posts publicly available, and the next thing that has anything to say about SFF is r/sffpc.

Other option is just getting your own domain + webspace + installing some kind of gallery software or just WordPress and abusing it as image gallery :D

cu, w0lf.