How does PCIe work?

[Carlos1010]

Hello everyone and as you may know i'm a noob,

So I am trying to make a new computer this fall and I really don't understand this: What is PCIe express and what is PCIe or PCIe 3.0? What is the difference?

Then another big thing what is 16x or 8x and what's the difference? How do you know if your GPU has it or if the PCIe has it? 

I think I need a person with a big response in order for me to understand or at least link as website but I prefer an explanation. Thanks for reading and thanks for the reply!

[Enderman]

the "e" stands for "express"

https://en.wikipedia.org/wiki/PCI_Express

[NinjaJc01]

PCIe is a connector. It's on motherboards. PCIe 16x is the connector used for GPUs. It has 16 data lanes. 8x has half that, 1x, 2x and 4x follow that logic as well. With each generation of PCIe, the bandwidth doubles, so a PCIe 3.0 8x has the same band width as a PCIe 2.0 16x. At the moment, no GPU is held back by PCIe bandwidth.

[Carlos1010]

so for example if you put a 16x GPU in a 8x PCIe slot you get have the speed/bandwidth?

[Kryis]

PCI-E is a physical interface on a motherboard, it replaced AGP and PCI as the main connector for graphics card, this is due to the much higher bandwidth it provides.

 

1.0, 2.0 and 3.0 are all versions of PCI-E, each one faster the last. Most GPUs now run on 3.0, I believe amd motherboard still only use 2.0 or so (Correct me if i'm wrong)

 

x16, x8, x4 is the current bandwidth mode you're running, this is dependent on the number of PCI-E lanes you have. If you have a single card then it should always be running at x16, if you have dual cards it will most likely run at 16 for one and 8 for the other, unless you have intel CPU with 40 PCI-E lanes, most CPUs have 28.

 

That's the basics of it anyhow.

 

[Kryis]

3 minutes ago, Carlos1010 said:

so for example if you put a 16x GPU in a 8x PCIe slot you get have the speed/bandwidth?

You'd get half the bandwidth, but it is unlikely to affect your GPU if it's PCI-E 3.0 due to PCI-E 3.0 x8 is as fast as PCI-E 2.0 x16

[thekeemo]

2 minutes ago, Kryis said:

PCI-E is a physical interface on a motherboard, it replaced AGP and PCI as the main connector for graphics card, this is due to the much higher bandwidth it provides.

 

1.0, 2.0 and 3.0 are all versions of PCI-E, each one faster the last. Most GPUs now run on 3.0, I believe amd motherboard still only use 2.0 or so (Correct me if i'm wrong)

 

x16, x8, x4 is the current bandwidth mode you're running, this is dependent on the number of PCI-E lanes you have. If you have a single card then it should always be running at x16, if you have dual cards it will most likely run at 16 for one and 8 for the other, unless you have intel CPU with 40 PCI-E lanes, most CPUs have 28.

 

That's the basics of it anyhow.

 

You forgot to mention that x16 x8 x4 also depends on the wiring of the socket

[stconquest]

See, when a GPU and a motherboard fall in love...

 

Sorry, I am bored.

[Kryis]

10 minutes ago, thekeemo said:

You forgot to mention that x16 x8 x4 also depends on the wiring of the socket

Yeah, and  you can get sockets that are smaller that run at x1 and x4

Example

Also, a x16 socket can run at x8, x4 and x1. This means you can install a x1 card(wireless etc)

 

[Carlos1010]

Wait isnt the pcie slots referred to the motherboard not the CPU?

[thekeemo]

1 minute ago, Kryis said:

Yeah, and  you can get sockets are are smaller that run at x1 and x4

 

Also, a x16 socket can run at x8, x4 and x1. This means you can install a x1 card(wireless etc)

I mean a x16 physical slot that is only x4 electrically for example

[MightyMic]

2 minutes ago, Carlos1010 said:

Wait isnt the pcie slots referred to the motherboard not the CPU?

Not exactly sure what you're trying to say. But, the CPU will only support a certain number of pcie lanes. Intel's new i7 6950X supports 40 lanes, whereas the i7 6700k only supports 28 lanes. How ever a motherboard can have more or less lanes. It's up to the manufacturer.

[Clanscorpia]

9 minutes ago, Kryis said:

PCI-E is a physical interface on a motherboard, it replaced AGP and PCI as the main connector for graphics card, this is due to the much higher bandwidth it provides.

 

1.0, 2.0 and 3.0 are all versions of PCI-E, each one faster the last. Most GPUs now run on 3.0, I believe amd motherboard still only use 2.0 or so (Correct me if i'm wrong)

 

x16, x8, x4 is the current bandwidth mode you're running, this is dependent on the number of PCI-E lanes you have. If you have a single card then it should always be running at x16, if you have dual cards it will most likely run at 16 for one and 8 for the other, unless you have intel CPU with 40 PCI-E lanes, most CPUs have 28.

 

That's the basics of it anyhow.

 

Low end Intel boards use 2.0. My granny's H81M-E34 had 2.0

[Kryis]

2 minutes ago, thekeemo said:

I mean a x16 physical slot that is only x4 electrically for example

Don't they normally decrease the slot size to match the x8, x4 etc ? Haven't seen a full length socket be limited to anything but x8 or x16.

 

I know most SLI / Crossfire boards will have PCI-E like the following (These are the max speeds and ignoring physically smaller slots)

I have seen ones that provide full x16 but unsure how or why.

 

PCI-E x16

PCI-E x8

PCI-E x16

PCI-E x8

[Carlos1010]

3 minutes ago, MightyMic said:

Not exactly sure what you're trying to say. But, the CPU will only support a certain number of pcie lanes. Intel's new i7 6950X supports 40 lanes, whereas the i7 6700k only supports 28 lanes. How ever a motherboard can have more or less lanes. It's up to the manufacturer.

What do you mean lanes, what is that?

[MightyMic]

1 minute ago, Carlos1010 said:

What do you mean lanes, what is that?

x16, x8, x4 etc. (sixteen lanes, eight lanes, four lanes, etc.)

[Kryis]

4 minutes ago, Carlos1010 said:

What do you mean lanes, what is that?

https://en.wikipedia.org/wiki/PCI_Express#Lane

[Carlos1010]

 

2 minutes ago, MightyMic said:

x16, x8, x4 etc. (sixteen lanes, eight lanes, four lanes, etc.)

So your saying there is 40x slots?

[thekeemo]

7 minutes ago, Kryis said:

Don't they normally decrease the slot size to match the x8, x4 etc ? Haven't seen a full length socket be limited to anything but x8 or x16.

 

I know most SLI / Crossfire boards will have PCI-E like the following (These are the max speeds and ignoring physically smaller slots)

I have seen ones that provide full x16 but unsure how or why.

 

PCI-E x16

PCI-E x8

PCI-E x16

PCI-E x8

Nope

Look at the crossfire only boards

X16

X4

and maybe a few x1

[MightyMic]

2 minutes ago, Carlos1010 said:

 

So your saying there is 40x slots?

No, right now on consumer based board the max is x16

[straight_stewie]

PCIe 3.0 works like this. But ignore all that engineery stuff that nobody really knows anyway. All you need to know is that it's a connector on a motherboard that is used to connect internal devices to the "bus". You get a number of "lanes" which basically represent the bandwidth of communication with whatever card is in the slot. The higher the number of lanes, the more bandwidth the card gets.

For example:

• We will be using a GIGABYTE G1 Gaming GA-Z170X motherboard.

 

The Motherboard has 3 PCIe x16 slots, but they function in the following manner: When 1 slot is populated it functions in x16 mode. When 2 slots are populated both slots function in x8 mode. When 3 slots are populated they function in x4 mode.

So in a build with a single graphics card, that graphics card will get "x16" amount of bandwidth. When using two graphics cards (say in an SLI/crossfire setup), each card will only see half of that bandwidth, as it will be operating in x8 mode. This means that per card internal I/O performance will be highest when the least amount of PCIe slots are used. Generally with graphics cards running two makes up for this loss in I/O performance.

This motherboard also has 3 PCIe x1 slots, on a separate bus from the x16 slots. What this means is that if we put a graphics card in a PCIe x16 slot, and an audio card in one of our x1 slots, the graphics card will still function in x16 mode even though we have two PCIe slots populated.  

This brings me to my next topic: In each generation of the PCIe specification (1.0, 2.0, 3.0) there are two types of slots: a x1 slot and a x16 slot. The x1 slots are the short ones, and the x16 slots are the long ones. As previously discussed, a x16 slot may run in less than x16 mode if certain conditions are met. 

This is actually quite a complex topic that deserves a thread all it's own, but I hope that this helps you in some way.
@Carlos1010

[Carlos1010]

And how much exact bandwidth does a x16,x8,x4,x1 have? Because i've seen curtain like sound cards that need like 500 bandwidth or something

[Kryis]

4 minutes ago, thekeemo said:

Nope

Look at the crossfire only boards

X16

X4

and maybe a few x1

Well, it's never a good day unless you learn something.

[straight_stewie]

3 minutes ago, Carlos1010 said:

500 bandwidth ofsomething

If you can find an example of the exact thing you are referring to, that would help us to explain.

[Kryis]

3 minutes ago, Carlos1010 said:

And how much exact bandwidth does a x16,x8,x4,x1 have? Because i've seen curtain like sound cards that need like 500 bandwidth ofsomething

As long as it's PCI-E 2 or 3 you'll be fine and don't need to worry about bandwidth.