Question Can a PCIe Riser Card be used in the end of a PCIe Extension Cable?

Brian McG

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I am thinking of doing a SFF Build in a DIY Case, that will use a PCIe Gen 4.0 Extension Cable to mount a GPU vertically.

Since most GPUs will not use the full bandwidth of PCIe Gen4.0, let alone 5.0 when that becomes available, I was wondering - should it be possible to put a Riser Card in the end of an Extension Cable in order to sneak in a couple of extra PCIe slots into the build? I haven't been able to find a Cable with more than one Slot at the end.

If so, can anyone recommend suitable Cables and/or Risers? It will be a low-profile build. So there will be physical space for 4 slots.

I appreciate that all the slots will have to share the same bandwidth of the orriginal slot. But this should not be much of a problem given the PCIe bandwidth now available.
 

Lutfij

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You could look into Sliger system's riser cables(that are bifurcated, which were on their older SFF chassis') but I think they've been discontinued due to bandwidth issues.

should it be possible to put a Riser Card in the end of an Extension Cable in order to sneak in a couple of extra PCIe slots into the build?
Perhaps I'm interpreting it the wrong way, what are you looking for exactly? A riser cable with more bifurcated lanes or a riser cable that's long enough to migrate your device to any part of a chassis?
 

Brian McG

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My intention is to use an Extension Cable to rotate the GPU through 90deg and mount it alongside the Motherboard. Since I can't find an Extension Cable with more than one card slot already on it, I was wondering if I could use a Riser Card with more Slots plugged into the end of the Cable.

As I understand it, even a high-end GPU will only use half the capacity of of PCIe x16 Gen4.0. So there should be enough bandwidth available. (Since I'm not intending to do anything until Ryzen 5 launches in 2024, PCIe Gen5.0 should be availalable by then.)

Again, correct me if I'm wrong, but I think Bifurcation is a Motherboard function. So that's something I'll have to bear in mind when chosing the Motherboard.
 

Karadjgne

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So you want use a pcie add on board in the x16 slot, then plug storage into that board as well as the riser cable for the gpu to piggyback storage and gpu from the same x16 slot since the gpu will only be running 4.0 x8 (3.0 x16 and only use 3.0 x8) anyway?

That's not going to work out as intended. Physically it's possible, but you then assume that the storage is also only going to be running at 3.0 x16 bandwidth, and there's also an assumption of power through that board since most gpus have a slot power requirement. You are also going to rely on the cpu pcie lanes not being full while the gpu and storage are being simultaneously accessed.

You'll end up with a higher power draw than the card is intended for and bandwidth getting flip-flopped, which is going to create issues with smooth fps.
 
My intention is to use an Extension Cable to rotate the GPU through 90deg and mount it alongside the Motherboard. Since I can't find an Extension Cable with more than one card slot already on it, I was wondering if I could use a Riser Card with more Slots plugged into the end of the Cable.
List full specs of your system.

Since you're talking about PCIE 4.0 extension cable, then I'm guessing you have PCIE 4.0 board and PCIE 4.0 graphics card. Correct?
If you're putting raiser at the end of extension cable, then raiser has to be PCIE 4.0 certified also.
Or else you can expect PCIE signal quality issues.
 

Brian McG

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So you want use a pcie add on board in the x16 slot, then plug storage into that board as well as the riser cable for the gpu to piggyback storage and gpu from the same x16 slot since the gpu will only be running 4.0 x8 (3.0 x16 and only use 3.0 x8) anyway?

That's not going to work out as intended. Physically it's possible, but you then assume that the storage is also only going to be running at 3.0 x16 bandwidth, and there's also an assumption of power through that board since most gpus have a slot power requirement. You are also going to rely on the cpu pcie lanes not being full while the gpu and storage are being simultaneously accessed.

You'll end up with a higher power draw than the card is intended for and bandwidth getting flip-flopped, which is going to create issues with smooth fps.
I'm not wanting to add storage - just the option to add in additional PCIe cards.
 

Brian McG

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List full specs of your system.

Since you're talking about PCIE 4.0 extension cable, then I'm guessing you have PCIE 4.0 board and PCIE 4.0 graphics card. Correct?
If you're putting raiser at the end of extension cable, then raiser has to be PCIE 4.0 certified also.
Or else you can expect PCIE signal quality issues.
I cannot list full specs of System, as it does not yet exist, Indeed the answer to this question might help determine the specifications of the system required to support it. I'm in no hurry. I'm planning my new build for Ryzen 5 in 2024!

But, yes, you are right. a Riser would need to be PCIe 4.0 certified as well. The problem currently is I can't find any. I was hoping someone would know of a firm that produced such a thing.

However after 56 years in the business, I'm fairly used to my ideas being 'out there'.

Hopefully if I ask the question of sufficient maunufacturers of Riser Cards, I'll to prompt someone to do something. So far I've asked: SuperMicro and AmeriRack. Any Ideas of who else to ask>
 
found here pcie gen 4, can be run as x4x4x4x4 or x8x4x4 or x8x8 or x16
https://www.ioi.com.tw/products/proddetail.aspx?CatID=106&DeviceID=3050&HostID=2108&ProdID=1060249
here is host device, its using slimSAS connectors (cables here SFF-8654)
then here are pcie slots
2xSFF-8654 to 2x x4 slots
2xSFF-8654 to 1x x16 slot (x8 bandwith)
4xSFF-8654 to 1x x16 slot (x16 bandwith)
they also offer 2xSFF8654 to 2x M2 slots

first link also shows you how its wired and what not with pictures

edit: pcie slots will need 3.3V, so make sure you have 3.3V on your sata power cables, as most consumer PSUs have those missing, its 5th wire on sata cable
 
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Brian McG

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found here pcie gen 4, can be run as x4x4x4x4 or x8x4x4 or x8x8 or x16
https://www.ioi.com.tw/products/proddetail.aspx?CatID=106&DeviceID=3050&HostID=2108&ProdID=1060249
here is host device, its using slimSAS connectors (cables here SFF-8654)
then here are pcie slots
2xSFF-8654 to 2x x4 slots
2xSFF-8654 to 1x x16 slot (x8 bandwith)
4xSFF-8654 to 1x x16 slot (x16 bandwith)
they also offer 2xSFF8654 to 2x M2 slots

first link also shows you how its wired and what not with pictures

edit: pcie slots will need 3.3V, so make sure you have 3.3V on your sata power cables, as most consumer PSUs have those missing, its 5th wire on sata cable
Thanks for that. Just what I was looking for. I like the flexibility it offers too.
 

Brian McG

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Jan 23, 2015
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Thanks for that. Just what I was looking for. I like the flexibility it offers too.
found here pcie gen 4, can be run as x4x4x4x4 or x8x4x4 or x8x8 or x16
https://www.ioi.com.tw/products/proddetail.aspx?CatID=106&DeviceID=3050&HostID=2108&ProdID=1060249
here is host device, its using slimSAS connectors (cables here SFF-8654)
then here are pcie slots
2xSFF-8654 to 2x x4 slots
2xSFF-8654 to 1x x16 slot (x8 bandwith)
4xSFF-8654 to 1x x16 slot (x16 bandwith)
they also offer 2xSFF8654 to 2x M2 slots

first link also shows you how its wired and what not with pictures

edit: pcie slots will need 3.3V, so make sure you have 3.3V on your sata power cables, as most consumer PSUs have those missing, its 5th wire on sata cable
SORRY. I thought this was a solution, but it's not - for me anyway. You see I'm trying to fit everything into a low-profile case with the PCIe Slots rotated 90deg to show off the GPU. That means I need to fit all the Slots into 80mm. But the PCIe Slot Expansion Boards only have one Slot and are 40mm high. So I'd get two boards in OK - BUT the GPU would be taller than the Case, as it would overhang the top expansion board - not what I was hoping for.

I'd need a single PCIe Riser Card with two or three PCIe Slots on it at the regular 18mm spacing. That would enable me to have double-slot GPU at the top and one or two PCIe Slots below it.

I like the SlimSAS Connectors though, as I have them passing over a HDPLEX 250W GaN Passive AIO ATX Power Supply on the way to the GPU. Since PSU is 94% efficient is will only be giving off 15W at max load. Nevertheless I'm planning to use a thermal heat pad under it to use the aluminium base of the case as a heat sink. I'd also prefer not to block the airflow over it.
 

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