Explain PCI E

[Wink]

PCI-Express 3.0/2.0 x16 Slots (run at x16 or dual x8 or x8/x4/x4)

 

So what exactly does this mean? I tried googling and only understood it seems to mean that this is a potential point of bottlenecks

 

Thanks in advance guys.

[DIV1D3]

If one card is inserted than it will run at x16, 16 lanes, if 2 cards are inserted than they will get x8 each, if three are inserted than one will get x8 and the other two will get x4. It can only handle 16 lanes at one time so that is why they are split up to one card (x16, x0, x0), 2 cards (x8, x8, x0), 3 cards (x8, x4, x4).

[Hans Christian | Teri]

If one card is inserted than it will run at x16, 16 lanes, if 2 cards are inserted than they will get x8 each, if three are inserted than one will get x8 and the other two will get x4. It can only handle 16 lanes at one time so that is why they are split up to one card (x16, x0, x0), 2 cards (x8, x8, x0), 3 cards (x8, x4, x4).

That's a pretty great and easily understandable explanation, good job.

[DIV1D3]

That's a pretty great and easily understandable explanation, good job.

Thanks , it's nice to hear good remarks from fellow techies. 

[Osmium]

Also PCIe 3.0 16 lanes are a lot better than PCIe 2.0 lanes. (PCIe2.0 16x lane roughly equals PCIe 3.0 8x). Pretty much all GPUs today do not need 3.0 16x and there is hardly any performance hit going to 8x.

[D3MON]

a pcie 16x slot (wether its pcie v1.0, v2.0, v3.0) is the typical slot a graphics card will go into.

PCIE is just a for of bus, a bus being like a motorway/highway along which data/cars travel.
the more lanes the bus/highway/motorway has the more bandwidth you have.

when people talk about 8x they are talking about about how many lanes that slot has, an 8x slot is half the length of a 16x slot, a 4x is half of an 8x slot and the smallest you'll find is typically 1x, this is usually for devices that dont require a ton of bandwidth like soundcards and some low end raid cards or even wifi cards.

you CAN get pcie 16x slots.....that only have 8x lanes, if you look in these slots you wil see that the wires that the graphics/sound card touches only go half way along, this is so you can add in a full length graphics card into the slot without having to modify it, it will however only get half the bandwidth.

when people talk about a board having 16x, 8x, 8x, that means that board will likely have 3 or 4... 16x length slots and you could potentially run 3 or 4 graphics cards in that system, however, the first slot is full bandwidth 16x, the next one is half bandwidth at 8x and the next one below that is also 8x half bandwidth.

there is only so many lanes of bandwidth on a given chipset and it has to be divided up,say you made a chipset with 32 lanes, you could have 2 16x slots and run 2 graphics cards, you could have 4 8x slots and run 4 8x raid cards, or you could run 32 1x sound cards...
you could if you wanted have all 4 16x length slots capable of holding a long graphics card but only wire them to 8x.

knowing that a chipset only has so many lanes board manufactures divvy up the bandwidth as you add devices, so if you have 1 card it might run at 16x, if you add in another graphics card they both run at 16x, if you add another card the top runs at 16x then the bottom 2 run at 8x, and if you add in a 4th card all cards will go down to 8x bandwidth.

pcie 2.0 is twice the bandwidth of pcie1.0, and pcie 3.0 is twice the bandwidth of pcie 2.0..
so a pcie 2.0 16x slot has the same bandwidth as a pcie 3.0 8x slot...

so if you have 4 graphics cards in a pcie 3.0 system at 8x speed, thats like having 4 graphics cards in a pcie 2.0 system with all of them at 16x.

now heres the bit that causes allot of questions and amd vs intel rivalry, intel chipsets (and now amd) support pcie 3.0 speeds but at the moment we dont have much need for this much bandwidth, the difference between having 2 gtx titans on pcie 2.0 16x/16x and pcie 3.0 16x/16x isnt measurable.

having 4 titans in pcie 2.0 8x/8x/8x/8x on something like a gigabyte 990fx-a ud7 might only be 5% (margin of error) behind the same system with a 4960x on a rampage 4 extreme at pcie 3.0 16x/8x/8x/8x.

I dont think I've ever written a short explanation on this forum...

oh and yes you can run a pcie v3.0 graphics card in a pcie v1.0 16x slot like 7870 or whatever in an lga 775 board and you wont notice any difference as pointed out above.