PCI-E Lanes available?

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Bloody Chainsaw

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I am looking to build a new budget pc, with a 7th gen intel cpu (probbaly core i3 7100 or core i5 7500) but cant seem to figure out the pcie lanes divison. ARK says, the cpu's have 16 lanes for use, while the H270 chipset has 20 and the b250 chipset has 12. I am curious that in the B250, will the motherboard cap the available number of pcie lanes from the cpu? And in the H270, will it be the cpu capping the motherboard instead?
Plus i read somewhere that the chipset reserves 4 lanes for sata and usb? Is this correct?

 
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ko888


If you're using a Z270 chipset motherboard that would be true.

The B250 and H270 chipsets don't split the 16 lanes that are dedicated to the primary PCIe x16 slot. All 16 lanes are always dedicated to the primary discrete graphics card. The second card in the CrossFire set gets its 4 PCIe lanes from the B250 or H270 chipset.
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ko888

ko888

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Don't confuse the 16 PCIe lanes wired to the CPU socket for the graphics card with the 12 PCIe lanes on the B250 chipset. They are two separate PCIe busses.

Intel_B250_Chipset_Block_Diagram.jpg
 
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Yamitime

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The Cpu lanes (16) 3.0 are different to the chipset lanes . Basically the 16 lanes of the cpu are used to communicate with the pci-express .They can be split into 1x16 or 2 x8 etc for one or two gfx cards .The motherboards lanes are what the manufacurer uses for addons like wifi usb lan etc. The more lanes the chipset has the more ad-dons are usually installed in the board
 
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Bloody Chainsaw

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So does this mean that if i install, say a 2-way Crossfire along with an NVMe on a board with a 16-lane CPU, the split will be x8/x4/x4, and i wont be able to install anymore PCI-E based stuff like a WLAN card?
 
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Bloody Chainsaw

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Ummm.....are you saying that the motherboard and cpu add up to give like 36 lanes? Or so how does the motherboard provide lanes if they were reserved by the chipset? Please clarify.....kinda novice on this.
 
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ko888

ko888

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H270: 16 + 20 = 36 lanes

B250: 16 + 12 = 28 lanes

The PCIe lanes on the chipset may be shared with other devices connected to the chipset. On some motherboards the PCIe x4 slot shares two of its lanes with a SATA Express connector. If the SATA Express connector is being used then the PCIe x4 slot will only have 2 lanes active.

You need to read the specific motherboard's specifications to determine how it is allocating the chipset's PCIe lanes. A B250 chipset motherboard would have a greater likelihood of having shared PCIe lanes.
 
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Bloody Chainsaw

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Yeah, kinda aiming for crossfire in the long run. But this question is basically to test the superiority in pcie lanes for the B250, H270 and Z270 chipsets, and to see which supports cross.fire
 
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Bloody Chainsaw

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So, when i connect Crossfired GPUs to a 16 lane cpu, does that mean that the graphics card run at x8/x8 and the M.2 SSDs and other PCI-e stuff run on lanes from the motherboard, in fact meaning that i am utlizing over 20 lanes?

 
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ko888

ko888

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If you're using a Z270 chipset motherboard that would be true.

The B250 and H270 chipsets don't split the 16 lanes that are dedicated to the primary PCIe x16 slot. All 16 lanes are always dedicated to the primary discrete graphics card. The second card in the CrossFire set gets its 4 PCIe lanes from the B250 or H270 chipset.
 
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