CPU PCI-E Lanes

[JaZoN_XD]

Say you are running a CPU that supports 16 PCI-E lanes and you are using two nVIDIA cards in SLI (8X/8X).

 

What would happen if you put another PCI-E based card in? (e.g. Network adapter, sound card, SSD etc.)

[WinNut]

If you plug those cards into the 1x slot, the lanes are coming off the chipset, not the CPU.

[slightlyjaded]

Say you are running a CPU that supports 16 PCI-E lanes and you are using two nVIDIA cards in SLI (8X/8X).

 

What would happen if you put another PCI-E based card in? (e.g. Network adapter, sound card, SSD etc.)

Depends on what else you have in your system. Thing like a PLX chip, and the chipset itself quite often give you  a few extra lanes to play with.

[johnny5c]

The PCH (chipset) provides an additional 8 lanes for low bandwidth peripherals so your GPU's will still run at 8x/8x.

[JaZoN_XD]

Depends on what else you have in your system. Thing like a PLX chip, and the chipset itself quite often give you  a few extra lanes to play with.

 

 

The PCH (chipset) provides an additional 8 lanes for low bandwidth peripherals so your GPU's will still run at 8x/8x.

assuming the mobo is a standard sli mobo without a fancy plx chip. (SOOO EXPENZIVVVEEEE)

[gcubed]

You can't put 10 lbs. of shit in a 5 lb. bag. But as others have indicated, just because your CPU is rated for 5 lbs., that doesn't mean 5 lbs. is your limit because other things come with their 5 lb. bags also. Having said that, if you fill up the additional bags and continue shoveling, your rig will take on a distinct air.

[Sintezza]

PLX chips are just one big Fairytail

But it works.

[slightlyjaded]

PLX chips are just one big Fairytail

But it works.

It's closer to creative scheduling. Your PCIe lanes are very rarely saturated with data. PLX chips Pretend to give you extra lanes by scheduling the tasks in such away that the extra data slots in when it can. (I could be wrong, but that's my rather simplistic understanding of how they work

[gcubed]

It's closer to creative scheduling. Your PCIe lanes are very rarely saturated with data. PLX chips Pretend to give you extra lanes by scheduling the tasks in such away that the extra data slots in when it can. (I could be wrong, but that's my rather simplistic understanding of how they work

 

It is as close as it needs to be. PLX chips, at their core, are switches. They turn a card's access to the PCI-E lanes on and off. It could be thought of as hyperthreading for the PCI-E lanes.

 

@JaZoN_XD

Look, there is no clear answer to your question, because your question is somewhat unclear.

If you are asking if you start adding PCI-E cards to the system, will it eventually fail. The answer is, yes. At what point, depends on the CPU, the motherboard and the cards you are adding. The motherboard's manual will have the information.

 

With anything that is recent (Z97 or better), 2-way SLI/Crossfire and two or three PCI-E v2.0 cards would probably work (again, RTFM). And of course, there are some absolute beast combinations out there that would allow 4-way SLI and additional PCI-E cards.

[JaZoN_XD]

It is as close as it needs to be. PLX chips, at their core, are switches. They turn a card's access to the PCI-E lanes on and off. It could be thought of as hyperthreading for the PCI-E lanes.

 

@JaZoN_XD

Look, there is no clear answer to your question, because your question is somewhat unclear.

If you are asking if you start adding PCI-E cards to the system, will it eventually fail. The answer is, yes. At what point, depends on the CPU, the motherboard and the cards you are adding. The motherboard's manual will have the information.

 

With anything that is recent (Z97 or better), 2-way SLI/Crossfire and two or three PCI-E v2.0 cards would probably work (again, RTFM). And of course, there are some absolute beast combinations out there that would allow 4-way SLI and additional PCI-E cards.

Alright, sorry I didn't include this before.

 

Say the motherboard has 2 PCI-E 3.0 slots and 1 PCI-E 2.0 Slot

Let's say there are 2 or 3 more PCI-E 1X slots.

The motherboard's PCI-E configuration is this: 16X/0X/0X           8X/8X/0X           8X/4X/4X

The motherboard does not have a PLX chip.

The two PCI-E 3.0 slots are populated with nVIDIA GPUs which uses ^ (8X/8X/0X)

If I plug in a PCI-E 3.0 1X device in one of the 1X slots or the PCI-E 2.0 slot (or maybe multiple 1X devices) what will happen/will the computer still work?

 

Sorry if I'm just repeating my question uselessly all over again.

[gcubed]

Based on the information you have given, I would say that you have saturated your PCI-E 3.0 lanes. But good news, PCI-E is forwards and backwards compatible (sorta kinda). Basically, a PCI-E 3.0 card will be perfectly happy (normally) in a PCI-E 2.0 slot (it should function as if it were a PCI-E 2.0 card). It is conceivable that a card could require a 3.0 connection and something like that would not work.

 

In theory, you can mix and match version 1.0, 2.0 and 3.0 PCI-E cards and slot. That is to say a 1.0 card can work in a 3.0 slot and the other way around. In practice that is not always the case (as in with gfx cards).

Additionally, 1x cards will work in 16x slots (also, 4x and 8x if you can find any on the board). This also works going the other way, you can in theory plug a 16x card into a 1x slot (this requires a bit of unprofessional professionalism. something like a dremel, and a total disregard for the mobo warranty).

 

 

Please Note: SLI and Crossfire are additional standards that USE PCI-E and have their own requirements. From what you have said, 2-way SLI will work in your system, but 3-way and 4-way never will.

 

Another thing. It is conceivable that this PCI-E 3.0 1x card may require a PCI-E 3.0 lane. Normally, they don't and it is only a recommendation (this largely depends on the nature of the card). But if it is indeed required, you may wish to consider a different card.

 

 

{Edit}

Another, another thing. When I say that plugging the PCI-E 3.0 1x card into another PCI-E 3.0 slot not working, I don't mean to say that the computer would fail to boot. In all probability it would boot up in a 8x/4x/4x configuration. This would essentially leave you with a working computer, BUT...

SLI requires 8x for all cards in the SLI array, so you would have a working computer that had SLI disabled and no way to enable it.

[Glenwing]

Alright, sorry I didn't include this before.

 

Say the motherboard has 2 PCI-E 3.0 slots and 1 PCI-E 2.0 Slot

Let's say there are 2 or 3 more PCI-E 1X slots.

The motherboard's PCI-E configuration is this: 16X/0X/0X           8X/8X/0X           8X/4X/4X

The motherboard does not have a PLX chip.

The two PCI-E 3.0 slots are populated with nVIDIA GPUs which uses ^ (8X/8X/0X)

If I plug in a PCI-E 3.0 1X device in one of the 1X slots or the PCI-E 2.0 slot (or maybe multiple 1X devices) what will happen/will the computer still work?

 

Sorry if I'm just repeating my question uselessly all over again.

Guess I'll give the simple answer since no one else seems to want to.

The CPU provides 16 PCIe 3.0 lanes, these are usually used for x16 slots. However this is not the only source of PCIe lanes. The motherboard chipset also has 8 PCIe 2.0 lanes for auxiliary functions.

x1 slots are wired through the motherboard chipset, and as such they won't affect the CPU lanes. Therefore you can still run x8/x8 graphics cards along with an x1 card.

The x4 slot is PCIe 2.0, which means it's still routed through the motherboard chipset, so there will be no difference if you plug an additional card into that slot as well.

[JaZoN_XD]

Based on the information you have given, I would say that you have saturated your PCI-E 3.0 lanes. But good news, PCI-E is forwards and backwards compatible (sorta kinda). Basically, a PCI-E 3.0 card will be perfectly happy (normally) in a PCI-E 2.0 slot (it should function as if it were a PCI-E 2.0 card). It is conceivable that a card could require a 3.0 connection and something like that would not work.

 

In theory, you can mix and match version 1.0, 2.0 and 3.0 PCI-E cards and slot. That is to say a 1.0 card can work in a 3.0 slot and the other way around. In practice that is not always the case (as in with gfx cards).

Additionally, 1x cards will work in 16x slots (also, 4x and 8x if you can find any on the board). This also works going the other way, you can in theory plug a 16x card into a 1x slot (this requires a bit of unprofessional professionalism. something like a dremel, and a total disregard for the mobo warranty).

 

 

Please Note: SLI and Crossfire are additional standards that USE PCI-E and have their own requirements. From what you have said, 2-way SLI will work in your system, but 3-way and 4-way never will.

 

Another thing. It is conceivable that this PCI-E 3.0 1x card may require a PCI-E 3.0 lane. Normally, they don't and it is only a recommendation (this largely depends on the nature of the card). But if it is indeed required, you may wish to consider a different card.

 

 

{Edit}

Another, another thing. When I say that plugging the PCI-E 3.0 1x card into another PCI-E 3.0 slot not working, I don't mean to say that the computer would fail to boot. In all probability it would boot up in a 8x/4x/4x configuration. This would essentially leave you with a working computer, BUT...

SLI requires 8x for all cards in the SLI array, so you would have a working computer that had SLI disabled and no way to enable it.

I already knew that you can dremel the end of a PCI-E slot and fit another card onto it (lel i breakz mi mothabord) and wow, that was a lot of information but thanks a lot. 

Guess I'll give the simple answer since no one else seems to want to.

The CPU provides 16 PCIe 3.0 lanes, these are usually used for x16 slots. However this is not the only source of PCIe lanes. The motherboard chipset also has 8 PCIe 2.0 lanes for auxiliary functions.

x1 slots are wired through the motherboard chipset, and as such they won't affect the CPU lanes. Therefore you can still run x8/x8 graphics cards along with an x1 card.

The x4 slot is PCIe 2.0, which means it's still routed through the motherboard chipset, so there will be no difference if you plug an additional card into that slot as well.

Yes. Thank you for the simple answer. I think I like that better.