Understaning PCIe 16x/0x/16x/0x/8x vs 8x/8x/8x/8x/8x

[bostondriver]

I'm trying to understand what my options when looking at MB specs describing PCIe 3.0 slots.

I notice PCIe slots described as (using 5 slots as an example) 16x/0/16x/0x/8x or 8x/8x/8x/8x/8x.

I think I understand enough if all slots were to be used for Video cards (or at least enough to do the next level of research.) In my case, I'm looking at just one PCIe 3.0 16x adapter.

What happens if I use the other slots for non video? Can I assume 16x/0x/8x/8x/8x even though the MB spec doesn' list this or will the video card performance be impacted due to using one of the other slots as non 16x? Most likely these will be 1x PCIe 2.0 cards (more Ethernet, WinTV video capture, other assorted toys etc.)

Is this MB specific or apply for any MB?

Thanks

 

[Eximo]

It is more chipset specific then motherboard, but it can vary from board to board. The only boards that support 5 8x ports have a secondary PCIe bridge chip (PLX).

You pose an interesting scenario, honestly I am not sure. Motherboard manuals will have a chart of supported configurations. While it may have the bandwidth it may not be able to manage it due to addressing.

 

[bostondriver]

I was hoping the answer would help me pick MB/Chipset <g>

I don't think we've reached the point where everything needed comes bundled with the MB; PCIe slots allow the flexibility to add additional NIC's, second sound card etc.

 

[Eximo]

There aren't a lot of devices that take advantage of 8x ports, mostly SATA/RAID/SAS controllers. Most NICs make due with 1x, fancy use 4x.

z87 PCIe 3.0 x16/x0, 8x/8x + PCIe 2.0 8x/0x/0x/0x, 4x/1x/1x/1x, 1x/1x/1x/1x

z77 PCIe 3.0 x16/x0, 8x/8x + PCIe 2.0 (16x slot @ 4x)/1x/1x/1x

(most common)X79 PCIe 3.0 x16/x16/x0, x16/x8/x8 + PCIe 2.0 1x/1x

(some boards)X79 PCIe 3.0 x16/x16/x0, x16/x8/x8 AND 1 PCIe 3.0 x16 @ 4x + PCIe 2.0 1x/1x

PLX X79 4 x PCIe 3.0/2.0 x16 (x16 or dual x16/x16 or x16/x16/x16/x16) *3 x PCIe 3.0/2.0 x16 (x8 mode)

EATX PLX X79 boards

7 (PCIE1/PCIE2/PCIE3/PCIE4/PCIE5/PCIE6/PCIE7: x16/0/16/0/16/0/16 mode or x16/8/8/8/8/8/8 mode) (2 x PLX PEX8747 Bridges to support 4-Way SLI in Gen3 x16/16/16/16 mode)

Now the chip is still limited to its 40 PCIe with X79 and 32PCIe lanes with Haswell/Ivy Bridge, so while you can plug in all the cards you want, they will have interrupts (extra clock cycles)to process data that exceeds that bandwidth limit.

There are also a few EATX PLX enabled Haswell and Ivy boards out there.

 

[bostondriver]

How about:

http://www.asrock.com/mb/Intel/X79%20Extreme9/?cat=Specifications

The manual lists only 16x/0x/16x/0x/8x or 8x/8x/8x/8x/8x as supported. I was hoping 16x/0x/8x/8x/8x would be supported too. Hence my original question.

For this rig, I need one PCIe 3.0 16x for video, and the rest of the slots will have various 1x PCIe 2.0 cards for things which the MB doesn't have, or doesn't have enough of.

I need LGA 2011 Ivy Bridge-E MB with Intel Core i7-4820K (minimum). The CPU/Chip sets MUST support vt-x, vt-d, and must support Linux (and hopefully FreeBSD) natively besides Win7 Pro.

Thanks

 

[ihog]

What graphics card are you looking at? Because chances are that it won't be hindered by PCIe 3.0 x8.

 

[Eximo]

I think if it could do ASRock would have listed it. Looks like it only has the two modes.

If that is all you need, just get a board with a few dedicated 1x slots, a lot cheaper too.

"(most common)X79 PCIe 3.0 x16/x16/x0, x16/x8/x8 + PCIe 2.0 1x/1x"

http://www.newegg.com/Product/Product.aspx?Item=N82E16813131800

 

[bostondriver]

What graphics card are you looking at? Because chances are that it won't be hindered by PCIe 3.0 x8.

I haven't decided yet. My questions are more for my understanding, so that in a year or two, I have flexibility to change a few things vs a new rig.

 

[bostondriver]

http://www.newegg.com/Product/Product.aspx?Item=N82E16813131800

That was my first choice, but ASUS doesn't support Linux and I'm not convinced that supports vt-d