Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
My PC appears to run games as I would expect it to, so maybe there's no real problem here.
However, when I run the Steam System Information tool, I notice that it says:
Primary Bus: PCI Express 2x
This ought to say "16x", right? But in my BIOS, there are no settings for PCI Express speed aside from selecting Auto/Gen 1/Gen 2/Gen 3. Above that selector is a greyed-out message: Speed 2x.
I cannot try another slot because this is a Micro ATX board, and the other 16x slot is too close to other plugs; the video card cannot fit there.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Just to be clear. Do you have the graphics card installed in the top most PCIe x16 slot or bottom one?
The Z170m-PLUS has one real x16 slot - which is the top one, while the bottom 'x16' slot is electrically x4 which may even run at x2 if other PCIe lanes from the PCH are being used up, e.g. for a M.2 SSD.
If you are using the top x16 PCIe slot, download and run GPU-Z, making sure to run the 'render test' and see what bus speed it reports.
If it's still x2, try reseating the graphics card or lightly cleaning the PCIe slot and card edge connector to dislodge dust etc.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Thanks for your help!
I don't know how long to run the render test for. It looks like it would carry on forever if I let it, or does it end by itself?
Anyway, here's how it looked after a few minutes:
http://gpuz.techpowerup.com/16/06/18/7ad.pnghttp://gpuz.techpowerup.com/16/06/18/2mj.png
Yes, the card is using the top slot (grey plastic, nearest the CPU). Due to the size of the card, that's the only place it can be plugged in. The other x16 slot is too close to other connectors.
ETA: Nothing else is connected by PCI-E. All SSDs/HDD connected via SATA.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
The render test just gets the GPU working to encourage the PCIe bus to run at its maximum, it only has to run while you're checking the PCIe bus interface rate.
The result is troubling, the card should be running at x16. The top PCIe slot on the Z170m-PLUS has its own dedicated x16 connection to the CPU so other components shouldn't affect it, unlike the other PCIe slots which are connected to the PCH.
Have you tried reseating the card yet? Giving the slot a good blast from a gas duster may help.
Dodgy PCIe connections have been known to cause cards to run at slower PCIe speeds.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Well I think I have to give up at this point. Yes, I did reseat and clean the points, but to no effect.
The weird thing is that the card is running Rocket League at somewhere above 60fps at 1440p (not sure where exactly as I have a 60Hz monitor), The Witcher 3 mostly in Ultra and High settings as per the GeForce Experience suggested settings for my card, etc. The only reason I noticed was because of a conversation I saw about recent changes in the Steam system specs for the average user, so I ran the test to see how my machine stacked up now, and that "2x" jumped out at me. If not for that, I wouldn't have been drawn to go and look. Unfortunately I have no other cards to test in the slot, but I'm going to hope it's something freaky in the card rather than the motherboard, for obvious reasons! I really don't want to have to return this motherboard and go through everything again with rebuilding the whole PC, not to mention the difficulties of not being able to use the PC (part of my job relies heavily on this computer too).
Thanks for giving the problem your attention: much appreciated.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
I think GPU-Z has always been a bit iffy about correctly identifying the bus width that the card is using. I've seen all sorts of odd stuff in it (including x16 PCIe 2 cards registering as, for instance, x1 PCIe 1 cards!). As long as the card is performing as expected in games and under load I really wouldn't worry about what bus type GPU-Z is registering.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Quote:
Originally Posted by
scaryjim
... As long as the card is performing as expected in games ...
But, what performance is to be expected?
The difference in performance between the bandwidth offered by PCIe x16 3.0 and x2 3.0 varies widely between games, it can be quite significant on some but unapparent on others;
http://www.techpowerup.com/reviews/N...press_Scaling/
I don't know what else to suggest, other than reseating the CPU, that doesn't involve swapping components :/
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Quote:
Originally Posted by
DDY
But, what performance is to be expected?
The difference in performance between the bandwidth offered by PCIe x16 3.0 and x2 3.0 varies widely between games, it can be quite significant on some but unapparent on others;
http://www.techpowerup.com/reviews/N...press_Scaling/
I don't know what else to suggest, other than reseating the CPU, that doesn't involve swapping components :/
I'm going to check again with some other friends. There's got to be someone who's got a spare card lying around... just everyone I tried so far is like me (sells when buying).
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Have you tried updating the BIOS? It maybe that it that they've fixed a speed reporting bug...
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
Are you sure its not just that CPU-Z doesnt update that field dynamically, and that when you first run it the card is running in a power saving mode?
When just displaying Windows, it would seem likely that the card only needs a small amount of bandwidth, so might switch to only using 2 lanes of the PCI-e bus.
Re: Why would my mobo read a 16x PCI Express slot as 2x? (ASUS Z170m-PLUS)
I have actually found CPU-z to be very accurate, if it has told me I am running x4, I have been.....at least when your running the render test.