Tom's Hardware > Forum > Graphic & Displays > Graphics Cards > PCI-EXPRESS X16 BACKWARDS COMPATIBILITY?

PCI-EXPRESS X16 BACKWARDS COMPATIBILITY?

Forum Graphic & Displays : Graphics Cards - PCI-EXPRESS X16 BACKWARDS COMPATIBILITY?

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mechluke   10-12-2006 at 09:37:54 PM

Guys my mobo supports pci-e video cards up to x4 speed.We all know that all the pci-e video cards are 16x.So will a pci-e x16 card work in my pci-e x4 mobo and with how much performance penalty if it does work...........?????????

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Anoobis   10-12-2006 at 09:42:35 PM
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Anandtech has some info for you.

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bliq   10-12-2006 at 10:10:15 PM
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Quote :

Guys my mobo supports pci-e video cards up to x4 speed.We all know that all the pci-e video cards are 16x.So will a pci-e x16 card work in my pci-e x4 mobo and with how much performance penalty if it does work...........?????????



I assume you're using one of those PCI-E/AGP boards from ECS or Asrock.

The video card will work and the performance penalty is negligible according to something I read at anandtech. Today's video cards, even the most powerful ones aren't really saturating the PCI Express bus yet (I've read there's little difference in performance from x1 to x16 for even high end video cards)

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doggykyle   10-12-2006 at 10:12:15 PM
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x16 and x4 aren't speeds. They signify the amount of Tx/Rx serial lanes there are to that PCIe slot. That means a x16 video card has 16 Tx and 16rx data lanes and needs that many supported on the motherboard (chipset). However, if you had a x16 motherboard, you could plug in a x4 card and the other 12 lanes are tri-stated.

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bliq   10-13-2006 at 02:11:48 AM
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Quote :

x16 and x4 aren't speeds. They signify the amount of Tx/Rx serial lanes there are to that PCIe slot. That means a x16 video card has 16 Tx and 16rx data lanes and needs that many supported on the motherboard (chipset). However, if you had a x16 motherboard, you could plug in a x4 card and the other 12 lanes are tri-stated.



That may be, but it doesn't change the fact that x1/x4/x16 slots all seem to support x16 video cards at essentially the same level of performance, meaning perhaps, video cards only utilize one lane or at least can only approach saturating one lane if lane use is dynamic.

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Mach5Motorsport   10-13-2006 at 05:40:34 AM
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Quote :

x16 and x4 aren't speeds. They signify the amount of Tx/Rx serial lanes there are to that PCIe slot. That means a x16 video card has 16 Tx and 16rx data lanes and needs that many supported on the motherboard (chipset). However, if you had a x16 motherboard, you could plug in a x4 card and the other 12 lanes are tri-stated.



That may be, but it doesn't change the fact that x1/x4/x16 slots all seem to support x16 video cards at essentially the same level of performance, meaning perhaps, video cards only utilize one lane or at least can only approach saturating one lane if lane use is dynamic.

You are forgetting that there are some PCIe boards that are in fact 8x in their throughput capacities, even in SLI mode.

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bliq   10-13-2006 at 09:03:30 AM
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My understanding is that they operate at/with x16 when only one card is installed. When a second card is installed, half the capacity is allocated to the second card. I don't know about SLI but my crossfire board has a continuity card that fits in the second slot when running only one card.

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