Pci 16x/8x for CF

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Peterr Peter

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Jun 6, 2013
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installed CF 2x7970 today .... its a good upgrade , BUT i have a problem .... i have the asrock extreme 4 z87 MB (socket 1150) and realized that if i have a single gpu the pci-e slot will work at 16X but with 2 gpu`s the 2 pci-e slots will be working at 8x/8x (not even 16x/8x) . Thats a big dissapointment for me :(
My questions are : is there a noticable diff between pci-e 16x and 8x
What socket 1150 MB could i buy for a better performance (16x/16x or 16x/8x)

excluding the evga z87 ftw classified that is not even out and would be out of my price range
 
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Titan
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May 18, 2007
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The GPU slot PCIe lanes are fed directly from the CPU and the only options without an expensive PLX PCIe switch are x16 or x8x8 or x8x4x4.

A motherboard with a PLX switch which multiplexes the CPU's only x16 interface into x16x16 adds around $150 to motherboard cost so motherboards with one of those on-board usually cost over $350. If the EVGA FTW was already out of your price range, forget about motherboards with the PLX switch.

Performance-wise, we are talking about 2-5% in most cases between x8x8 and x16x16 on PCIe 3.0.
 
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Peterr Peter

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Jun 6, 2013
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10,530
so its not worth it .......i`m going to stick to my asrock extreme 4 then :)) the only problem now is the heat that the cards are spreading in the case .....
thanks for answering my problem guys ;)
 
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Titan
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May 18, 2007
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The PCIe 3.0 lanes on LGA1150/1155/2011 motherboards are not "supported" by the chipset, they are attached directly to the CPU. The chipset has absolutely nothing to do with it beyond just happening to be whatever goes with a particular CPU/socket and z?7 being "required" to unlock CPU PCIe controller lane splitting on LGA1150/1155 i5/i7 CPUs. This is why so many PCIe 2.0 (Sandy Bridge) boards can be upgraded to 3.0 with a simple BIOS and CPU (Ivy Bridge) upgrade - upgrading the CPU upgrades PCIe support on the main x16 slot(s).

On LGA1150/1155, the chipset PCIe lanes are 8xPCIe 2.0.
 
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Titan
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Are you talking about the chipset supporting the CPU or PCIe here? The chipset obviously must support the CPU but is not physically or electrically involved in the CPU's own PCIe support, which is why Sandy boards that can support Ivy CPUs gain PCIe 3.0 with a CPU upgrade even though the chipset (b6x/h6x/z6x) does not support PCIe 3.0 in any way, shape or form.
 
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Titan
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I already said that 2-3 messages ago: the chipset plays no part except unlocking the lame arbitrary lock Intel put on splitting the CPU's PCIe controller - the same lameness that is (supposed to) lock multipliers on K-chips when used with non-Z chipsets but that Intel fudged up in the 8x/Haswell series and plans to "fix" with a microcode update... the CPU supports it but the (non-Z) chipsets disable it just because they can. (Wouldn't that qualify as "tied-selling" under anti-trust and other protection laws? Forced to buy one premium product to unlock fundamentally unrelated functionality in another?)

In any case, non-Z chipsets still let eligible CPUs use PCIe 3.0. They just don't allow the CPU to do lane-splitting for SLI/CFX.
 
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