Can I use the second PCI Express x16 slot for my cpu without performance loss?

[gameideasred]

Hello dear people,

I own the x79-ud3 motherboard that has:
2 x PCI Express x16 slots, running at x16 (PCIEX16_1, PCIEX16_2)

I am going to replace my gpu with a bigger one and and there is not room for installing the new gpu in the first slot (x16) so I would need to install it in the second x16 slot (PCIEX16_2). Thereof, I started wondering:
Will there be ANY possible loss when installing gpu in PCIEX16_2 instead of PCIEX16_2?
Please do not sugar code anything.

Take a look at this(from the manual for x79-ud3):

Also, as you can see, they say: "For optimum performance, if only one PCI Express graphics card is to be installed,
be sure to install it in the PCIEX16 slot."
Notice that I have emphasized the - do you think they use the to refer to a certain one of the two PCI Express x16 slots or could they just have used the a instead of the, since there is no particular one of them that will result in better performance?

Thanks!

 

[JoshRC]

As long as its also an x16 then you shouldn't see any loss in performance.

 

[gameideasred]

JoshRC (do not know how to tag) - like 0.000%? The thing is that as stated in the manual (I will upload a pic of a relevant section of the manual), there ARE two PCI x16 slots, but I have always read that only the first one is the most optimal one.

 

[Satan-IR]

It's OK as mentioned above if the motherboard can run a dual setup (yours most probably can because you have to have either a Sandy Bridge-E or an Ivy Bridge-E CPU.

However, just to make sure if you're going to "replace" GPU with a bigger "one" why is first PCIE slot occupied? You can't use two different GPUs in the system unless they are identical to do SLI/CF. This being unlikely because you said it's a "bigger one".

What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot.

 

[gameideasred]

It's OK as mentioned above if the motherboard can run a dual setup (yours most probably can because you have to have either a Sandy Bridge-E or an Ivy Bridge-E CPU.

However, just to make sure if you're going to "replace" GPU with a bigger "one" why is first PCIE slot occupied? You can't use two different GPUs in the system unless they are identical to do SLI/CF. This being unlikely because you said it's a "bigger one".

What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot.

"What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot." - So what you are implying is that the first one can lead to better performance than the other x16 because that it is closer to the CPU?

Also, you can see from the image that I have uploaded what they recommend/say.

 

[Satan-IR]

It's OK as mentioned above if the motherboard can run a dual setup (yours most probably can because you have to have either a Sandy Bridge-E or an Ivy Bridge-E CPU.

However, just to make sure if you're going to "replace" GPU with a bigger "one" why is first PCIE slot occupied? You can't use two different GPUs in the system unless they are identical to do SLI/CF. This being unlikely because you said it's a "bigger one".

What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot.

"What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot." - So what you are implying is that the first one can lead to better performance than the other x16 because that it is closer to the CPU?

Also, you can see from the image that I have uploaded what they recommend/say.

It's not what I'm implying they explicitly recommend that (not necessarily because of proximity) but mainly because due to design/architecture some motherboards/chipsets share the system resources such as the PCI bus on the other PCIE slot with other controllers in the system such as SATA controllers for storage or other PCI/PCIE slost.

The sharing usually is not done on the first slot and therefore user can expect no hindrance to GPU performance if it's a single-GPU setup and not due to presence of other components/devices on the other PCIE slots/ports/lanes. That's why they recommend that.

But as I said mentioned before by JoshRC the second one is a X16 slot and if there's no other device/card in slot 1 or other slots it should work at X16. The shot from the specs page of the mobo clearly states that "The PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot. When the PCIEX8_2 slot is populated, the PCIEX16_2 slot will operate at up to x8 mode."

That means second X16 slot will not operate at X16 if there's a device present in PCIEX8_2 slot .

If you have one single GPU which I'm assuming is the case from what you said put it in PCIEX16_1.

 

[gameideasred]

It's OK as mentioned above if the motherboard can run a dual setup (yours most probably can because you have to have either a Sandy Bridge-E or an Ivy Bridge-E CPU.

However, just to make sure if you're going to "replace" GPU with a bigger "one" why is first PCIE slot occupied? You can't use two different GPUs in the system unless they are identical to do SLI/CF. This being unlikely because you said it's a "bigger one".

What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot.

"What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot." - So what you are implying is that the first one can lead to better performance than the other x16 because that it is closer to the CPU?

Also, you can see from the image that I have uploaded what they recommend/say.

It's not what I'm implying they explicitly recommend that (not necessarily because of proximity) but mainly because due to design/architecture some motherboards/chipsets share the system resources such as the PCI bus on the other PCIE slot with other controllers in the system such as SATA controllers for storage or other PCI/PCIE slost.

The sharing usually is not done on the first slot and therefore user can expect no hindrance to GPU performance if it's a single-GPU setup and not due to presence of other components/devices on the other PCIE slots/ports/lanes. That's why they recommend that.

But as I said mentioned before by JoshRC the second one is a X16 slot and if there's no other device/card in slot 1 or other slots it should work at X16. The shot from the specs page of the mobo clearly states that "The PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot. When the PCIEX8_2 slot is populated, the PCIEX16_2 slot will operate at up to x8 mode."

That means second X16 slot will not operate at X16 if there's a device present in PCIEX8_2 slot .

If you have one single GPU which I'm assuming is the case from what you said put it in PCIEX16_1.

Okay, so as a conclusion: It does matter whether I use PCIEX16_1 slot or PCIEX16_2 slot even though they both run as x16 and both will operate at x16 speed if I only has one gpu? :/

 

[Satan-IR]

It's OK as mentioned above if the motherboard can run a dual setup (yours most probably can because you have to have either a Sandy Bridge-E or an Ivy Bridge-E CPU.

However, just to make sure if you're going to "replace" GPU with a bigger "one" why is first PCIE slot occupied? You can't use two different GPUs in the system unless they are identical to do SLI/CF. This being unlikely because you said it's a "bigger one".

What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot.

"What's more, motherboard makers almost always recommend to use a "single" GPU in the first PCIE X16 slot which is the closest to the CPU slot. If the first one is used by another PCI component put that in PCIEX16_2 and the new GPU in the PCIEX16_1 slot." - So what you are implying is that the first one can lead to better performance than the other x16 because that it is closer to the CPU?

Also, you can see from the image that I have uploaded what they recommend/say.

It's not what I'm implying they explicitly recommend that (not necessarily because of proximity) but mainly because due to design/architecture some motherboards/chipsets share the system resources such as the PCI bus on the other PCIE slot with other controllers in the system such as SATA controllers for storage or other PCI/PCIE slost.

The sharing usually is not done on the first slot and therefore user can expect no hindrance to GPU performance if it's a single-GPU setup and not due to presence of other components/devices on the other PCIE slots/ports/lanes. That's why they recommend that.

But as I said mentioned before by JoshRC the second one is a X16 slot and if there's no other device/card in slot 1 or other slots it should work at X16. The shot from the specs page of the mobo clearly states that "The PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot. When the PCIEX8_2 slot is populated, the PCIEX16_2 slot will operate at up to x8 mode."

That means second X16 slot will not operate at X16 if there's a device present in PCIEX8_2 slot .

If you have one single GPU which I'm assuming is the case from what you said put it in PCIEX16_1.

Okay, so as a conclusion: It does matter whether I use PCIEX16_1 slot or PCIEX16_2 slot even though they both run as x16 and both will operate at x16 speed if I only has one gpu? :/

If it's a single GPU put it in PCIEX16_1 as recommended by manufacturer.

They both run at X16 if none other PCIE slot is occupied.

I pointed out before the manual says "The PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot. When the PCIEX8_2 slot is populated, the PCIEX16_2 slot will operate at up to x8 mode."

It's OK to put in PCIEX16_2 if no other slot is occupied but why not do what the board manufacturer recommends when possible?

 

[gameideasred]

@Satan-IR, okay, thank you so much for your time! But regarding your statement "but why not do what the board manufacturer recommends when possible?" - where do you see that they recommend to use the first slot? Don't they just recommend to use ONE OF the two pcie x16 slots, like where do you see that they refer to PCIEX16_1? Thanks again man, your time is very appreciated!

 

[Satan-IR]

No problem, glad to help. That's generally the case with many motherboards by various manufacturers as some boards treat the port farthest from the edge and closest to the PCU as 'primary' and other/s as 'secondary' in the motherboard/chipset architecture. Even if both can operate at X16 even when both are populated.

That's why as stated by the manufacturer in the shot from the manual you yourself uploaded the "the PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot" not the first one.

They don't know how users are gonna populate and use the ports, therefore they "generally" recommend the first PCIE slot because it doesn't "usually" share bandwidth with any other port/controller/device. Therefore, any future arrangement and population of ports/slots by the user (unknown to the maker of the board) would not hinder the performance of graphic card as long as it is in the first slot.

 

[gameideasred]

No problem, glad to help. That's generally the case with many motherboards by various manufacturers as some boards treat the port farthest from the edge and closest to the PCU as 'primary' and other/s as 'secondary' in the motherboard/chipset architecture. Even if both can operate at X16 even when both are populated.

That's why as stated by the manufacturer in the shot from the manual you yourself uploaded the "the PCIEX8_2 slot shares bandwidth with the PCIEX16_2 slot" not the first one.

They don't know how users are gonna populate and use the ports, therefore they "generally" recommend the first PCIE slot because it doesn't "usually" share bandwidth with any other port/controller/device. Therefore, any future arrangement and population of ports/slots by the user (unknown to the maker of the board) would not hinder the performance of graphic card as long as it is in the first slot.

Okay, so beside their implicit recommendation, it TECHNICALLY is the exact same performance that you get by using PCIEX16_1 and PCIEX16_2 if not any other slots are populated (i.e. you have a single cpu)? I know that you have stated all the facts needed to come up with a conclusion, but could you say yes or no to this one so that it cannot be any clearer ? ;-)

 

[Satan-IR]

Yes. In your case because it's a X79 platform and all relevant CPUs can manage 40 PCIE lanes for discrete GPUs, therefore, theoretically 2 X16 slots both running at full X16 speed are possible plus one slot running at X8 speed at the same time. 32 + 8.

Some chipsets also add some lanes for other PCIE devices such as network adapters and so on through the chipset.