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Hey guys.

I've been looking around places, and I've found these adapters that seem to split a single PCI-E 16x slot into two PCI-E 8x slots.

They look like this.
http://www.supermicro.com/a_images/products/Accessories/RSC-R2UT-2E8R.jpg

As you can see, on the bottom is a standard PCI-E 16x slot, and on the top is two PCI-E 16x slots that are running at 8X speed.

They're fairly expensive (http://www.ebay.com/itm/NEW-Supermicro-RSC-R2UT-2E8R-Riser-Card-/320906472140?pt=US_Computer_Disk_Controllers_RAID_Cards&hash=item4ab7842acc). (80 bucks on ebay) But I noticed one VERY IMPORTANT thing that they say about it.

https://i.imgur.com/BVMPeNT.png

The adapter is PASSIVE! If you look at the photo, there doesn't seem to be much circuitry on the board!

This leads me to believe that the PCI-E spec allows for passive splitting of lanes into at least two slower-speed lanes. The only problem is that normally, this is mechanically impossible. But what if you were to buy a couple of these...

https://i.imgur.com/l9aPDar.png
http://www.ebay.com/itm/Powered-PCI-E-16x-16x-Riser-Cable-with-Molex-/111078375273?pt=LH_DefaultDomain_0&hash=item19dcc97f69

And then cut up the cable, and re-wire it to split one slot into two or more lower speed slots?

Once power draw problems are resolved. I think it would be EPIC for running a crapton of mining cards on a single system at very low cost. But only if the PCI-E spec actually allows it.

What do you think? Does anyone know? I haven't seen anything like this done before, so I don't know how well it would work.

~Re

Only one way to find out ;D.

YEAH! *gets enthused*

Except I don't have the money to buy a bunch of risers. :P

I always wanted to try this, or even the pci-e risers for servers.  I'm surprised with all the need for adding as many cards to a board that nobody has engineered a cheap solution that has like 16 ports.  I've seen the rackmount pci-e servers for GPU processing, but they are redonkulous expensive.

Yeah. If this could be maass-manufactured. It could cost pennies per unit and be sold at reasonable prices for quite big profit.

Its not completely passive. A PCIE x16 slot has 16 data lanes, but only 1 set of control signals. Each x1 slot requires a set of control signals.

See pinouts:

http://pinouts.ru/Slots/pci_express_pinout.shtml

Silly question: why does it have to be passive?

And if it has to be passive, would this work: http://www.ebay.com/itm/NEW-Supermicro-RSC-R2UG-2E4E8-Riser-Card-/320906465389

I have no idea. But maybe. Too expensive to be worth it, though.


It doesn't have to be passive. It's just that if it is possible for it to be passive, it will allow for simple wiring of riser cables to work.


I see. What is it for, anyways? Keeping timing in sync? and if so, Is it not possible to share the "control signals"?

Why do you need a powered riser? NO! NO! NO!.

Besides, the adapter already has a PCI-E power plug for supplemental power. Theres your power right there.

it's not passive, there are microcontrollers on the board.
https://i.minus.com/iioM8kDylUlHY.png

It's listed as passive. Perhaps the microcontroller isn't important. Anyways, someone else here showed another one that is fully passive.

I'm not completely certain... SMBus signals can be shared via a simple splitter, and I'm not sure if JTAG is necessary, but Reference Clock is going to need some circuitry to be split, and something probably needs to be done to the detect signals. I haven't read the PCI-E spec, so I'm going off pinouts and some guesses only.

The problem is: does the Windows operating system recognising 10, 16 or more GPU?

virtualization.

I'm hearing reports of windows running with up to 13 GPU's. I have also heard that linux (which version or distro?) has a hard limit of 8 GPU's.

Subject to support in the bios or by the motherboard, I suppose.

Dude, your avatar kinda freaks me out.

On the other note - what's the point of "13 gpus" if your power supply cannot handle it?
Or you will have multi psu setup as well?

Obviously.

and try to stop looking at it. :P

It's way too expensive but I like the idea.

It looks like it's passive, as in doesn't need external power.  But it's obviously not as simple as a Y-connector.

You can get large PSUs that can handle lots of cards.

I can see where having a Cable Y adapter w/maybe an inline chip would be a great thing, because it would free up the limited motherboard selections that allow 4 or 6 GPU's

However, a main problem is the Windows OS + card drivers seem to currently be limiting the number of popular GPU cards to 6.

Linux has a hard limit of 8 cards. I see reports of people using 13 on windows.

Where you saw these reports? Thanks

Edit: I found it.

http://devgurus.amd.com/thread/158863

Original source is currently unavailable, but I have located i ton the web archive.

http://web.archive.org/web/20130429065445/http://fastra2.ua.ac.be/

If you Google for "diy vidock x2" you'll come across threads in which folks have combined 2 pcie x1 lanes into a single x2 connection for the purpose of connecting external videocards to laptops.  If they can do that, then surely we can do the reverse, right?  :)

Halfway down here: https://forum.lowyat.net/topic/2019705/all (https://forum.lowyat.net/topic/2019705/all) you can see a photo in which someone has cables plugged into two mini pcie connectors on a laptop motherboard.