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Author Topic: Passively splitting a single PCI-E 16x slot into 16 PCI-E 1x slots  (Read 27702 times)
ReCat
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June 17, 2013, 05:30:38 PM
 #1

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.


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. (80 bucks on ebay) But I noticed one VERY IMPORTANT thing that they say about it.



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...


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

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June 17, 2013, 05:46:16 PM
 #2

Only one way to find out Grin.
ReCat
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June 17, 2013, 05:59:42 PM
 #3

YEAH! *gets enthused*

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

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June 17, 2013, 07:01:59 PM
 #4

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.

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June 17, 2013, 07:04:55 PM
 #5

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

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June 17, 2013, 08:00:20 PM
 #6

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

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June 17, 2013, 08:36:39 PM
 #7

Silly question: why does it have to be passive?

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June 17, 2013, 08:37:43 PM
 #8

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

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June 17, 2013, 08:44:23 PM
 #9

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

Silly question: why does it have to be passive?

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.

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

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

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June 17, 2013, 09:40:43 PM
 #10

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.

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June 18, 2013, 12:23:47 AM
 #11

it's not passive, there are microcontrollers on the board.

It is pitch black. You are likely to be eaten by a grue.

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June 18, 2013, 01:01:00 AM
 #12

it's not passive, there are microcontrollers on the board.


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

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June 18, 2013, 01:24:58 AM
 #13

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

Silly question: why does it have to be passive?

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.

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

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

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.

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June 18, 2013, 09:15:19 AM
 #14

The problem is: does the Windows operating system recognising 10, 16 or more GPU?
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June 18, 2013, 02:33:27 PM
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The problem is: does the Windows operating system recognising 10, 16 or more GPU?
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June 18, 2013, 04:07:33 PM
 #16

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

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.

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June 18, 2013, 04:16:17 PM
 #17

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?


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June 18, 2013, 04:44:09 PM
 #18

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. Tongue

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June 18, 2013, 04:56:27 PM
 #19

It's way too expensive but I like the idea.
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June 18, 2013, 05:00:55 PM
 #20

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

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