PCI-e x16 slots down-rated by expansion cards other than video cards??

[lonkny]

Hey all, quick question - I own a RIIIE but can't find this discussed anywhere, and I don't think it is a question for just RIIIE owners, but a general question regarding motherboards... I realize the 1st and 3rd PCIE x16 slots are the 2 slots that should be used for pairs of SLI/XFire vid cards since they will continue to run at x16 speed with multiple graphics cards connected (check your motherboard manual to see which slots run at full x16 speeds w/multiple video cards connected). But what if you only have 1 video card and all other x16 slots are being used by other types of cards (RAID card, Sound card, etc.)? Or what if you have 2 vid cards in slots 1 and 3, but have the other two x16 slots filled as well, with other types of cards such as audio or RAID cards? Will plugging in peripheral cards like that also slow a slot down from x16 to x8?? Or will _only_ graphics cards in an x16 slot potentially lower its speed rating? From what I have been able to find in the manual & forums, it seems this is only applicable to video cards and not other types of cards, but I could definitely be wrong (hence why I'm writing! This is never explicitly discussed)... plz let me know what you all think, thx!

[sin0822]

it doesn't matter what the 3rd card is, you only have 32 lanes of PCI-E and with 2 GPUs and another PCI-E device it will reduce the bandiwdth to 16x,8x,8x.

[lonkny]

it doesn't matter what the 3rd card is, you only have 32 lanes of PCI-E and with 2 GPUs and another PCI-E device it will reduce the bandiwdth to 16x,8x,8x.

Good to know, thanks. However, you mention 32 total lanes being available - now this would be true with Video Cards b/c they would use as many lanes as were available to them... but what if you had x1 or x4 cards in the X16 slots? Would this allow your X16 card to remain at 16 lanes even if the other 3 slots were filled up with X1 and X4 cards?

Here's my situation - I have the Rampage III Extreme board with an ATI HD 5850 card in the first X16 slot. I have an PCI-E X1 network card (for Jumbo Frames support) in the X4 slot under the vid card, so that one is full. I have a USB/Firewire card in the PCI slot (for some odd reason Asus only gave the RIIIE 1 internal USB header! ). That leaves the 3 X16 slots available. I have an LSI MegaRAID PCI-E X8 RAID Controller card and an Asus Xonar Xense PCI-E X1 sound card.

For now, I have the X1 sound card in X16 Slot 2 and the X8 RAID Card in X16 Slot 4, leaving Slot 3 free (the 2nd "X16" video card slot). This would be the recommended configuration, correct?

Now, if I wanted to add another X1 or X4 RAID Card and fill up the last available X16 slot, would my video card run at X8, even though my cards are not utilizing all of the 32 available lanes? This is where I am unsure... I realize that adding a 2nd video card would force them all to X8, but what about another X1 or X4 card (adding an X4 card would leave me at 29 used lanes, IF the video card was allowed to run in X16 mode)? Any help is much appreciated, thx!!

[EniGmA1987]

Your board supports these configurations according to the manufacturer:

x16
x16/x16
x16/x8/x8 or 8x/8x/16x
x8/x8/x8/x8

I dont have this board and have never used it so I am just going off basic PCI-E knowledge and what the manufacturer says. But if you put a card in slot 2 it might run at 8x speed. It depends on how exactly the lanes can be configured by the board. It might be slots 1 and 3 can be 16x and slot 2 can only be a max of 8x. Or it might allow any slot to be 16x if there is only 1 or 2 cards installed and then split lanes as more cards get installed.
EDIT: according to a picture at techpowerup showing a closeup of the PCI-E slots, it looks like all contain full 16x electrical pins. So if only 2 cards are installed, they can be in any of the slots and still run at 16x speeds. That was where my confusion came from before, many boards do not have the full 16x electrical pins in the secondary PCI-E slots that get lanes split to them with multiple cards installed.


If you put a card in slot #3, it would run at 16x while the first 2 cards run at 8x or opposite depending on what the cards are. For example if you had an audio card and raid card in slots 1 and 2 and a graphics in slot 3 then the 3rd slot would run at 16x. But if you plugged them all in the opposite way then the graphics in slot 1 would run at 16x while the others had a max of 8x. If you then also put a card in the #4 slot, all slots run at 8x speeds.



In addition to those, it looks like the actual PCI-E 4x slot will continue to work at 4x speeds regardless of the other slot configurations.

[lonkny]

Thanks - I just ran GPU-Z to see where my video card stands right now, and it is still running at X16 (Bus Interface: PCI-E 2.0 x16 @ x16 2.0)... like I said I have peripheral cards in the 2nd and 4th slots right now (3rd slot is free). So I suppose I'll be OK as long as I leave that slot free.

Is there a utility available that shows how many lanes are in use/available for each PCI-E slot? Thanks again.

[lonkny]

So I just tested all this by adding another X1 sound card (Auzentech Forte 7.1) to the last remaining PCI-e X16 port, then booted up and ran GPU-Z, and lo & behold, the video card is _still_ running full 16 lanes on the primary X16 slot:



Note Bus Interface still reads PCI-E 2.0 x16 @ x16 2.0... correct me if I'm wrong, but doesn't this mean I am getting full 16 lanes for this card?

Just to recap, I have all 4 slots filled on a Rampage III Extreme, from top to bottom, with: ATI HD 5850 in Slot 1, Asus Xonar Xense PCI-E X1 in Slot 2, Auzentech Forte 7.1 PCI-E X1 in Slot 3, and LSI MegaRAID 9260 4-i PCI-E X8 in Slot 4.

If having all 4 PCI-E X16 slots filled with any card will slow all slots down to X8 each, why is GPU-Z showing X16? Please fill me in - looking forward to thoughts & ideas on this, thx!

[Falkentyne]

you cannot have something like a lane here, and a few lanes there, and then add a few more over in the next area. Your board supports these configurations:

x16
x16/x16
x16/x8/x8 or 8x/8x/16x
x8/x8/x8/x8


So if you have a card in the #2 slot, the first and second slot run at 8x speeds. Doesnt matter if it is a 1x, 4x, or 8x card. If you put a card in slot #3, it runs at 16x while the first 2 cards run at 8x. If you then put a card in the #4 slot, all slots run at 8x speeds.



In addition to those, it looks like the actual PCI-E 4x slot will continue to work at 4x speeds regardless of the other slot configurations.

Ok, I'm a bit confused.
How are you supposed to have two cards both running at X16, then? Based on what you told me, that's impossible, as you just contradicted yourself.

You said that X16/X16 is possible.
But then you said if a card is in the second slot, both 1st and second slot run at x8.

So what is that x16/x16 for if it's completely impossible for the second slot to run at X16?

[lonkny]

Good, at least I'm not the only one confused by all this I think what Enigma is saying is that cards in Slots 1 and 3 will run at X16, but cards in slots 1 and 2 will run at X8, which I don't think is correct... but Asus does state that if 4 _video_ cards are plugged in, the slots will all provide 8 lanes each. The question remains, does this apply to non-video cards as well? According to my test above, it seems to NOT apply, since my video card in Slot 1 is still at 16 lanes with the other 3 slots filled with other X1 and X8 cards... does anyone have something more definitive on all this?

Here is Everest showing the same, X16 on the video card with all 4 slots full (2 X1 sound cards & X8 RAID card):

[EniGmA1987]

It is because you are only using a single 16x and a single 8x card, all others are 1x. It doesnt have to split lanes anywhere when there is just a single 16x card in the system. If you were using a 16x video card and three 8x RAID cards then all would be running at 8x.

[mk-ultra]

yep since you're not maxing out your PCIE lanes, you get full speed(of the card) on each pcie port.

[lonkny]

That's what I thought/hoped, but the consensus wasn't in favor of this at first. Thanks for clearing things up.