GPU Rig Motherboard question. All PCIe 1x slots useable?

[NuSalvo]

I'm looking into building a GPU rig, already have a spare tower sitting in my other room that had a burnt out CPU.  It has an ASUS M4A79XTD EVO, with 2x PCIe 2.0 x16 and 2x PCIe x1.  Does that mean I can run 4 cards, right?  And I need to get risers (do they have to be powered?) for the 2 x1 slots also, correct?

I was just looking at upgrading the board also, since he put this together a few years ago, but if it can handle 4 I should be OK for right now.  I got a good deal on a 7970 so I'm going to make this an all-in-one mining hub to control several cubes, some GPU's, and some worthless USB sticks

Also, if I have multiple cards can I run guiminer/cgminer multiple times with parameters for litecoin and one for another scryptcoin at the same time?  Or is it all the cards at once per program?

[Loki-L]

PCIe is designed so that in theory basically any device can connect via any number of lanes with the bandwidth limited by whatever is lowest.

You can put an x1 Card in an x16 slot and it will work fine and you can put an x16 card into a slot that only has 8, 4 or 1 lanes and it will work albeit with only half, a quarter or a sixteenth of the bandwidth. In theory you could file open the end of the slow to allow cards with longer connectors in shorter slots but a riser seems like a smarter idea in practice.

Many motherboards have a second x16 slot that actually only works with 8 lanes and only is x16 in length so that people can put larger cards in there without having to file anything down.

Generally the number of lanes in total even with risers is limited by the PCIe controller which in modern computers is in the CPU and in slightly older ones in the chipset. Even server level Intel Xeon CPUs only provide 40 lanes worth of PCIe per CPU.

[NuSalvo]

So if I'm understanding this correctly, one card in the 16x slot takes up 16 lanes?  And I know if there is 2 cards in x16 slots, they both operate at x8 or still 16 lanes right? 

I have an AMD Athlon II X4 on the way, and from what I found the motherboard offers 38 PCIe lanes (It has an AMD 790x).   So two cards an x8 is 16, and another 2 at x1 would only be 18 lanes in total, right?

It makes it seem like any x1 slots is a waste because it operates at 1/16 then.  Is there a way to see what the 7970 would hash at in a x1 slot?

[pokerFace2]

I know plugging GPU card to PCIe 1x has no speed impact for Bitcoin mining. Im not sure about Scrypt mining, never tried it

[akuma6099]

I mine scrypt (LTC,BQC,WDC...) speed is not an issue when side by side. I have a gigabit GA-MA78G-D3SH Phenom X4 9750. It was designed for SLI back in 2008ish. My primary card runs at x16 and the secondary runs at x4. I have the same speed if I flip the cards around. In fact if you look around you'll notice that some people have riser cards. These cards convert your super short PCIe x1 slot into a powered x16 slot. The speed will of course operate at x1 but the work being done inside the GPU and GPU RAM is not affected by this. I believe the card cannot produce hashes fast enough to need more bandwidth. Your basically plopping a job on the stack and the card works through it and transfers the answer back. GPU workload is not based on how fast you can load work onto the card but how fast can the card push through the work. That is the bottleneck. So x1 shouldn't matter, but keep reading the forums for a consensus. Or someone correct me if I'm wrong.

Your PCIe slots are based on the motherboard chipset. They used to be North bridge, South Bridge but now Intel and the others are producing PCH(HUBs). We have 1 chip instead of 2. This chip is what has the USB, PCIe, PCI, I2C, SPI, UART, DMI, SMBios, RTC, GPU...... all of the busses and devices. The best place to start when trying to determine how the slots are tied together is your manufactures manual for that board. It will tell you if SATA ports 4+5 are shared with the Primary IDE controller and how your PCIe slots operate together. Here is a blurb from my board.


    1 x PCI Express x16 slot (Note 3), running at x16 (PCIEX16_1)
    1 x PCI Express x16 slot, running at x4 (PCIEX4_1) (The PCIEX16_1 and PCIEX4_1 slots conform to PCI Express 2.0 standard.)
    3 x PCI Express x1 slots (The PCIEX1_2 and PCIEX1_3 slots share the same PCIe bus with the PCIEX1_4 slot) (Note 4)
    2 x PCI slots

[NuSalvo]

Thanks alot akuma, that cleared up most of my questions.  I found my manual here,   http://support.asus.com/download.aspx?SLanguage=en&m=M4A79XTD+EVO&os=29  , but I can't seem to find anything about sharing controllers or what not, just something on page 37 (2-17) about IRQ shared assignments (which shows all the PCIe devices share D with the USB controller) and then page 38 shows the slots as PCIEx16_1, x16_2, x1_1, x1_2 but nothing about what slot they are on... 

[akuma6099]

The info is on page 38 section 2.5.6 You have a primary slot that runs at x16(Blue x16_1) 8GB/s = PCIe 2.0 standard for x16 link speed, and a Universal slot x16(Gray 16_2) with a max speed of 4GB/s -or- x8 link speed. It says max x8 link in the picture. The best test will be to plung in both cards and run GPUz tool. It will tell you your speeds, clocks, and temps. Either way, still no problems For more info on PCIe > https://www.icc-usa.com/compare-pci

[zmhaha]

I can firmly tell you that you can use the x1 slot with a riser without any loss of kh/s.
But make sure you get at least 2 powered riser just in case the mobo it sell can't provide enough powers to all 4 cards.
Since you have 2 x16 slots, 2 x1 slots, I would just get powered riser for the x1 slots.
But the prices on these things ain't that different, so you may as well just get all powered ones

[spartan82]

I can confirm I have a few miners running all with 16x and 1x slots, they make no difference with hashrate. Use powered risers to be on the safe side, although two of my miners have been running constant 9 months now easy with unpowered risers and no issues there. Maybe im just lucky