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Graphics card: PCIe3.0 x1 works but PCIe2.0 x16 doesn't?

cortlillard

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May 16, 2014
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Hello all,

You all have been very helpful to me so far on my Server to Desktop build here and here, and I have another question. The problem is that it the server MOBO has two PCIe x8 slots, and I still cant tell if they are 1.0 or 1.1 compatible.

I did some pretty extensive research on backwards compatibility of PCIe 1.0, 2.0, 3.0, and gambled with a 3.0 card working in my build. I purchased a Zotac 60607 PCIexpress 3.0 graphics card which has a x1 connector, and it works great in my build. (additionally I am a bit confused on if this is actually a 3.0 card)

I also did some more research on if a x16 card will work in an x8 slot, and with the amount of posts saying that it would, thought that it would without any problem. I wanted a bit more performance than a GeForce GT610, so I got a MSI n640-1gd5/lp which has a GeForce GT640 chipset and a 2.0 PCIe x16 connector.

The problem is that the motherboard wont recognize the 2.0 card at all. It powers up (fan is spinning), but the boot sequence/BIOS wont display on the card, and it does not show up in Device Manager in Win7 once booted. Boot up works just fine on the Zotac, so I am confident that I have selected the correct BIOS settings to boot over PCIe rather than onboard video.

My question is, if I return the MSI card, what would be a better option for use in a PCIe x8 slot that apparently supports 1.0 and 3.0 cards, but not 2.0 without having to just keep trying different cards until one works?

Thanks in advance guys!
 

Cats869

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Aug 16, 2014
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I'm a bit confused by your question, hopefully I understand what you're trying to ask.

[strike]All PCIe graphics cards are backwards compatible. It has always been like this... not sure what the future holds but currently, they are backwards compatible with whatever PCIe version it is on the motherboard. [/strike]

As long as the motherboard supports the physical x16 connector, you can plop a x16 PCIe card in the lane. If you have a PCIe x16 lane, any PCIe size card will fit in there, assuming it can fit in your computer case as well.

If you have a physical PCIe x8 lane which is half the size of the x16 lane, any card that has a x1, x2, x4, x8 will fit in that physical lane.

So tell me, you only have two PCIe x8 slots or do you have a x16 lane since it seems like you do have an x16 lane since you manage to get the GT 640 card in there. I'm not sure how you were able to fit an x16 card into an x8 lane unless they have one of those PCIe lane converters which I have never seen yet.

You can try a Radeon HD 7750 card and see how that goes. It's a 3.0 PCIe card but again, I don't really see how the motherboard cannot support 2.0 but can support 3.0.

CORRECTION: I forgot to strike through some stuff I said earlier. Anyway, what should have been said is that not all gen 3.0 cards will work in 1.1 lanes though generally speaking, they should be compatible, with the exception of the 3.0 cards and 1.1 gen lane motherboards combination
 

cortlillard

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May 16, 2014
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First of all, thanks for the suggestion!

I don't think this is entirely true. This page describes that typically Nvidia cards are fully backwards compatible, but not ATI cards: http://www.overclock.net/a/the-final-answer-to-the-controversial-pcie-x16-version-compatibility
Yes, I have read the update at the bottom of this thread that says that all of them should be backwards compatible with a BIOS update, BUT, I do not have access to the newest BIOS flash for this mobo.


I have found quite a few threads saying that you can 'cut' the back end off of a pcie x8 slot and put in a PCIex16 card. The x16 card will just operate at a maximum bandwidth of x8 speed. This is described here: hardwaresecrets.com/article/Everything-You-Need-to-Know-About-the-PCI-Express/190/4
Some PCIex8 slots are even 'open-ended' to allow for a PCIex16 cards to be put in like this:


That being said, putting in the x16 card into a 'cut' open ended x8 slot did not work for me.

I honestly think this might just be a game of keep trying cards until one works... but i don't think amazon/newegg will like me very much if I keep returning Items.
 

Cats869

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Guess you learn something new everyday. Interesting articles, thanks for the share.

For the PCIe backwards compatibility. I'm not so sure whether or not it applies to all cases but I guess it might apply to some cases. I do recall testing a HD 7750 card which is a PCIe 3.0 x16 card into a PCIe 1.0 or 1.1 x16 slot in my 2004 HP desktop computer (AMD OEM Motherboard) just to make sure it works and it worked perfectly fine, booted up into windows, ran some benchmarks, stress test, no issues and that is an AMD card but who knows.



 
Aug 6, 2013
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It is not entirely true that "ALL PCIe graphics cards are backwards compatible".

e.g.
A pre-2.0 PCIe slot motherboard is unlikely to work with a PCIe 3.0 ATi/AMD type graphics card.
There may be a very small percentage of motherboards that will with a BIOS/Chipset update; but CERTAINLY not all when it comes to ATi/AMD. The NVidia ones have a lot more chance for sure.

Example?
I have an old XP rig (2006) with an Athlon x64 and a 512Mb ATi X1950 XTX (x16 PCIe 1.1) I wanted to update. So I bought a HD7770 (3.0 Bus) graphics card based on the advice I had seen.

But it wouldn`t work.
So, I updated the BIOS (that was a pain).
But it still didn`t work.
So, I bought another HD7770 and tried that.
But it still wouldn`t work.
I ended up putting the X1950 XTX back in and it still runs perfect. Even if it doesn`t compete with my Haswell i5 rig or my GTX 780 i7 Haswell rig.

I also discovered that VERY many other people have had similar problems with OLDER (1.1 Bus) Motherboards.






 

Cats869

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cortillard already explained it to me about the whole compatibility issue. Thanks though for sharing your experience. Whenever I got free time, I should do some experimentation with the PCIe 3.0 and 1.1 and such and maybe make a small list of what old motherboards can support the newer 3.0 gen cards.

Anyway, I guess one of my old OEM compaq desktop fits into that small percentage of being compatible as well as a friend of mine who has a Pentium D OEM desktop by Dell
 
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Mine that didn`t work is the Compaq Presario (Athlon x64) so most modern graphics cards would be bottle-necked; but the best I could install is something like a HD4870 X2). Not sure that its worth any more effort.

Note that I understand that NVidia cards are claimed to work in the 1.1 slot; but I found out about that after I bought two HD7770 cards. As I dont like changing driver types (with their associated software).

Anyway 2015 brings in the PCIe 4.0 Bus standard.

There is not a lot of info on Wiki about the main models which are generally affected. But my guess is that ten thousand graphics cards have been sent back to amazon over the issue.


 

Cats869

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Interesting, what model Compaq Presario did you use?

My model Compaq Presario was the SR1850NX. It also has the Athlon x64 (3700+ I believe) (though it has the BIOS 3.15 (most up to date which was released back in 2005, desktop came out in 2004).
 
Aug 6, 2013
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Compaq Presario
SR1000
Next line....
SR1519UK

(SR1519UK ~ "UK" = UK English model of the PC)

Its an Athlon x64 3700+ I think. (Single core [but can run XP x64 as option])

I have it as dual boot XP; but dont use XP x64 much, as I cant find a wireless Wi-Fi dongle for x64-bit XP.


 

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