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Will pci express 3.0 x16 card work in pci 2.0 x8 slot

Last response: in Graphics & Displays
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November 26, 2012 6:20:03 PM

I have this complex situation here.

Using
Motherboard: ASUS-P8Z77-V-PRO
Processor: i5-3570k (Ivy bridge)
Two graphic card: Both Diamond diamond radeon hd 7770

On website I saw the specifications as: "The two PCI Express 3.0/2.0 X16 slots are controlled by the CPU, with the first slot working at x16 when only one video card is installed and with both working at x8 when two video cards are installed. since these slots are controlled by the CPU, they will offer PCI express 2.0 bandwidth (8GB/s at x16) when a sandy-bridge CPU is installed but PCI express 3.0 bandwidth (16 GB/S at X16) when an IVY bridge CPU is used"

My question is:
1) Since I have an IVY bridge which gives 3.0 bandwidth and a motherboard which converts the PCIE slots to 2.0 x8 (if two video cards are present) what will are my PCIE slots (2.0 or 3.0)?
2) Can I use my video card Diamond diamond radeon hd 7770 whose specs are: PCIe 3.0 16x ?

Thanks,

Sal
a c 84 U Graphics card
a b à CPUs
November 26, 2012 6:23:39 PM

1. the slots will run at 3.0 x8
2. yes you can.
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a b U Graphics card
a b à CPUs
November 26, 2012 6:45:48 PM

As long as it is physically x16 in length, then x8 is fine. 7770 aren't going to max out those slots anyway even at x8 bandwidth.
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November 26, 2012 10:04:04 PM

Thanks guys .. So these video cards have to be connected by a cross-fire bridge? Please tell me if I am making any mistake here. I assembled the configuration:

Motherboard: ASUS-P8Z77-V-PRO
Processor: i5-3570k (Ivy bridge)
Two graphic card: Both Diamond radeon hd 7770

Then I installed vista-64 bit home edition and booted the computer with iGPU. Installed the drivers for the Diamond radeon hd 7770 (with catlyst controller) and restarted the computer. On this restart I went into bios disabled the iGPU and let it boot. The problem is my second video cared is showing up in display adapter and is shown by TechpowerupGPU. However the monitor connected to doesn't light up.
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Best solution

a c 84 U Graphics card
a b à CPUs
November 26, 2012 10:40:55 PM

is crossfire enabled in CCC (or amd vision center w/e)? if you have monitors connected to both cards, crossfire has to be disabled...

edit also you could try to following: first uninstall the drivers, power down, remove the second card, boot up, install the drivers, power down, plug in the second card, boot up...

and if everything fails, try the cards one by one, just to make sure they both work.
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a b U Graphics card
a b à CPUs
November 26, 2012 10:55:24 PM

Yes
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November 26, 2012 10:56:41 PM

Works great! Thanks a lot. But why should the crossfire be disabled if monitors are connected to both the card?
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November 26, 2012 10:56:52 PM

Best answer selected by sqsalman.
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a c 84 U Graphics card
a b à CPUs
November 26, 2012 11:06:03 PM

sqsalman said:
Works great! Thanks a lot. But why should the crossfire be disabled if monitors are connected to both the card?

afaik in crossfire setups all monitors have to be connected to the 'master' card... just the way it is. They might have changed it in recent drivers though, seeing as nvidia doesn't have that limit anymore. You could try it and see if it works :) 

edit: hmm i read the posts again, and obviously it doesn't... I should go get some sleep..
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November 27, 2012 1:36:10 AM

Hi, Another issue here. After disabling the crossfire in CCC, my two monitors connected to two different graphiccards started working (VGA Output). However, the other HDMI port doesn't produce any output on either graphic cards. What could be the reason? Thanks in advance
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