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PCI-E / Mobo Question

Last response: in Motherboards
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December 6, 2010 10:25:42 PM

My system has an Asus Maximus Gene III mATX motherboard. The top full length PCI-E slot is occupied by an ATI 5850 that also covers up the lone 4X PCI-E slot (bummer) Below that I have an empty full length PCI-E slot and an occupied PCI slot (wi-fi card)

I'd like to buy a PCI-E sound card, but the only slot I have is the second full length PCI-E slot. I understand that this will work, but my concern is this. My motherboard is a P55 based board and I am concerned that installing a sound card (even if it's just a 1X PCI-E card) in my second full length PCI-E slot will clip the number of PCI-E lanes feeding my video card from 16 down to 8. I didn't buy this motherboard expecting to do an SLI/CF setup so I didn't really think much of the 16 lanes vs. 8 + 8 lanes issue. If I install a sound card in my 2nd full length PCI-E slot, what happens to my video card in the top slot currently being fed by 16 PCI-E lanes?

More about : pci mobo question

a b V Motherboard
December 7, 2010 6:59:09 AM

Its do-able. IF your lanes do get gclipped, its minimal...and the framerates won't be hampered cos of the PCI-E 2.0 slots. All PCI-E soundcards need a PCI-E x1 slot, electrically you'll need 1 lane. FYI - the 5850 is using 16 lanes, 8 lanes don't kill framerates.

Correct me if i'm wrong :p  you'll have NO issues!

Further proof:

Quote:
A PCIe card will fit into a slot of its physical size or larger, but may not fit into a smaller PCIe slot. Some slots use open-ended sockets to permit physically longer cards and will negotiate the best available electrical connection. The number of lanes actually connected to a slot may also be less than the number supported by the physical slot size. An example is a ×8 slot that actually only runs at ×1; these slots will allow any ×1, ×2, ×4 or ×8 card to be used, though only running at ×1 speed. This type of socket is described as a ×8 (×1 mode) slot, meaning it physically accepts up to ×8 cards but only runs at ×1 speed. The advantage gained is that a larger range of PCIe cards can still be used without requiring the motherboard hardware to support the full transfer rate, which keeps design and implementation costs down
** http://en.wikipedia.org/wiki/PCI_Express - scroll down to the middle where the DFI board pics at.
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December 7, 2010 4:38:59 PM

rodney_ws said:
My system has an Asus Maximus Gene III mATX motherboard. The top full length PCI-E slot is occupied by an ATI 5850 that also covers up the lone 4X PCI-E slot (bummer) Below that I have an empty full length PCI-E slot and an occupied PCI slot (wi-fi card)

I'd like to buy a PCI-E sound card, but the only slot I have is the second full length PCI-E slot. I understand that this will work, but my concern is this. My motherboard is a P55 based board and I am concerned that installing a sound card (even if it's just a 1X PCI-E card) in my second full length PCI-E slot will clip the number of PCI-E lanes feeding my video card from 16 down to 8. I didn't buy this motherboard expecting to do an SLI/CF setup so I didn't really think much of the 16 lanes vs. 8 + 8 lanes issue. If I install a sound card in my 2nd full length PCI-E slot, what happens to my video card in the top slot currently being fed by 16 PCI-E lanes?


You'll be just fine. PCI-e x16 cards don't even come close to maxmizing the potential throughput of the bus. Even if you place the card in the x8 slot you'll not notice a difference. The sound card itself doesn't utilize enough bandwidth to justify 4 parallel lanes (we're talking about 500MB/s PER LANE to justify that much real estate). If you calculate that PCI-e 2.0 generates 500MB/s of bandwidth per lane, and your card is occupying a 16x slot, you're talking about a maximum theoretical bandwidth of 8GB/s (or 64Gbps) of traffic. Considering that your sound card will use a fraction of this bandwidth to process audio (ie - 320kbps or less), I think you'll do just fine. :) 
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December 7, 2010 6:55:06 PM

I guess what I was unsure of was how many lanes would be available for my video card.
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a b V Motherboard
December 7, 2010 8:34:56 PM

This should answer your question

**Populating the second PCI-E 2.0 x16 slot triggers the slots to run in x8/x8 mode as they both are hardwired to the cpu (that offers the x16 lanes). The P55 offers the x1 lanes but in your case, the slot are inaccessible. So the CPU will share lanes with the soundcard and your 5850 will be running at x8 mode.
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December 7, 2010 11:04:44 PM

Best answer selected by rodney_ws.
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a b V Motherboard
December 8, 2010 6:02:47 AM

Thank YOU for the vote! What sound card are you getting anyway?
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a c 135 V Motherboard
December 8, 2010 7:33:14 AM

This topic has been closed by Maziar
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