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Video card bandwidth in PCIE3 slot of X570 Taichi?

Printed From: ASRock.com
Category: Technical Support
Forum Name: AMD Motherboards
Forum Description: Question about ASRock AMD motherboards
URL: http://forum.asrock.com/forum_posts.asp?TID=12198
Printed Date: 06 Mar 2021 at 10:51pm
Software Version: Web Wiz Forums 12.04 - http://www.webwizforums.com


Topic: Video card bandwidth in PCIE3 slot of X570 Taichi?
Posted By: shmerl
Subject: Video card bandwidth in PCIE3 slot of X570 Taichi?
Date Posted: 14 Aug 2019 at 7:02am
X570 Taichi manual says:


Quote Matisse: 3 x PCI Express 4.0 x16 slots (PCIE1/PCIE3/PCIE5: single at x16 (PCIE1); dual at x8 (PCIE1) / x8 (PCIE3); triple at x8 (PCIE1)/ x8 (PCIE3) / x4 (PCIE5)


Does it mean that single video card will operate in PCIe x16 mode only in PCIE1 slot? What will happen if I put it in PCIE3 slot? It would a better fit in my case. It won't operate at x16?

My CPU is Ryzen 9 3900X.



Replies:
Posted By: Ray62
Date Posted: 14 Aug 2019 at 2:06pm
Yes, only the PCIE1 has wired 16 lanes as in every AM4 board. See manual:
PCIe slots:
PCIE1 (PCIe 4.0 x16 slot) is used for PCI Express x16 lane width graphics cards.
PCIE2 (PCIe 4.0 x1 slot) is used for PCI Express x1 lane width cards.
PCIE3 (PCIe 4.0 x16 slot) is used for PCI Express x8 lane width graphics cards.
PCIE4 (PCIe 4.0 x1 slot) is used for PCI Express x1 lane width cards.
PCIE5 (PCIe 4.0 x16 slot) is used for PCI Express x4 lane width graphics cards


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Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: shmerl
Date Posted: 14 Aug 2019 at 2:09pm
Why are then PCIE3 and PCIE5 slots referenced as (PCIe 4.0 x16 slot) if they can't ever operate in x16 mode? That's a bit confusing.


Posted By: Ray62
Date Posted: 14 Aug 2019 at 3:35pm
They must be mechanically compatible for GPUs, even if they only use 8 or 4 lanes. But that is a very old thing for mainstream motherboards.

If you want more fully PCI Express x16 lanes slots, you have to use a Threadripper or Intel socket 2066 board.

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Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: gizmic
Date Posted: 14 Aug 2019 at 3:53pm
thats like saying why usb 1 doesnt do usb 3.0

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Posted By: ksquared
Date Posted: 14 Aug 2019 at 9:50pm
Originally posted by shmerl shmerl wrote:

Why are then PCIE3 and PCIE5 slots referenced as (PCIe 4.0 x16 slot) if they can't ever operate in x16 mode? That's a bit confusing.


Yes, I'd agree about being confusing. They are physical x16 slots, but won't operate as x16 slots.

To me, even more confusing is that once you use both PCIE1 and PCIE3, the PCIE1 slot then drops from the x16 and becomes an x8 mode. But I guess most (or all) video cards can still operate fine in the x8 mode?

So then, is it if you use PCIE1 and the PCIE5 slot, the PCIE1 slot will still drop from the x16 and become an x8 mode? That is the way I'd read the manual, but if you add up the potential 8+8+4 you have 20 lanes, so is it possible the PCIE1 slot would remain x16 and the PCIE5 slot as x4?



Posted By: Ray62
Date Posted: 15 Aug 2019 at 5:31am
Originally posted by ksquared ksquared wrote:


So then, is it if you use PCIE1 and the PCIE5 slot, the PCIE1 slot will still drop from the x16 and become an x8 mode? That is the way I'd read the manual, but if you add up the potential 8+8+4 you have 20 lanes, so is it possible the PCIE1 slot would remain x16 and the PCIE5 slot as x4?


PCIE1 and PCIE3 are connected to the CPU and use 16 lanes, either in 16-0 or 8-8 mode. The answer to your first question is no.
PCIE5 and M2_3 are connected with 4 shared lanes to the chipset, so only one can be used at the same time.
So, if M2_3 is not in use, the answer to your second question is yes.

-------------
Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: shmerl
Date Posted: 15 Aug 2019 at 9:38am
Originally posted by Ray62 Ray62 wrote:

PCIE1 and PCIE3 are connected to the CPU and use 16 lanes, either in 16-0 or 8-8 mode.


If both are connected to the CPU, what exactly prevents PCIE3 from operating in x16 with only one device in it? It shouldn't be hard to detect that only one device is in use, and not to split the bandwidth.


Posted By: Ray62
Date Posted: 15 Aug 2019 at 3:56pm
I agree, 0-16 mode sounds possible, but not mentioned in the manual.
ASUS X570 Strix Series for example offers the same.
16-0, 8-8, 0-8 mode is given for X370/X470/X570 boards since the beginning of the Ryzen platform. I don't know if there are any exceptions.

Ask Asrock support, if the PCIE3 slot has 16 or only 8 lanes wired.


-------------
Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: gizmic
Date Posted: 15 Aug 2019 at 5:37pm
flip the board around you'll see the pins are different on pcie1 and pcie3. if it only reaches half way its only wired for x8

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Posted By: gizmic
Date Posted: 15 Aug 2019 at 5:40pm
why are you worried on the slot speed you shouldnt have anything that could use it unless its some multi raid card



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Posted By: shmerl
Date Posted: 15 Aug 2019 at 10:09pm
Originally posted by gizmic gizmic wrote:

flip the board around you'll see the pins are different on pcie1 and pcie3. if it only reaches half way its only wired for x8


Heh, I already installed the board. So what exactly do you see on the above picture? The PCIE1 slot wiring is half covered by the shield. Is it the same as PCIE3 or more?


Posted By: shmerl
Date Posted: 15 Aug 2019 at 10:11pm
I guess if the width of the wiring on PCIE5 slot is x4, then PCIE3 is x8 only?


Posted By: shmerl
Date Posted: 15 Aug 2019 at 10:14pm
Actually, looking closer at that picture, you can see that it's indeed half the width for PCIE3 and quarter of it for PCIE5:



So I suppose this confirms, that PCIE3 is x8 only.


Posted By: Xaltar
Date Posted: 15 Aug 2019 at 10:24pm
Yes, it looks like PCIe3 is wired as an X8, x16 is wired across the whole length of the slot.

There shouldn't be any issues using PCIe3 for your GPU, even PCIe 3.0 x4 offers plenty of bandwidth for most modern GPUs. PCIe 4.0 x8 has roughly the same bandwidth as PCIe 3.0 x16 (the bandwidth roughly doubles with each new generation). Similarly, even the bottom x4 slot should be fine as it will perform roughly on par with PCIe 3.0 x8.

I hope this helps ;)

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Posted By: Ray62
Date Posted: 16 Aug 2019 at 4:43am
Originally posted by shmerl shmerl wrote:

Actually, looking closer at that picture, you can see that it's indeed half the width for PCIE3 and quarter of it for PCIE5:
So I suppose this confirms, that PCIE3 is x8 only.


   A picture says more than thousand words.

-------------
Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: ksquared
Date Posted: 16 Aug 2019 at 5:07am
OK, with the help from everybody here, I am beginning to understand.

Now, what I'm confused about is the specifications state it supports AMD Quad CrossFireX, 3-Way CrossFireX, and CrossFireX. I can understand the CrossFireX with two graphics cards, then both are going at x8 in PICE1 and PCI3.

So how do you do the Quad CrossFireX and the 3-Way CrossFireX? And what will the cards be going at? They all can't go at x8, so maybe with the 3-Way the cards drop to x4? But is the Quad CrossFireX then at x1 for all four cards? Doesn't that somewhat defeat the concept of CrossFireX, especially if everything drops back to x1?

Note: I'm not actually wanting to do any more than one graphics card, but it would be appreciated if I could get to understand it.


Posted By: gizmic
Date Posted: 16 Aug 2019 at 10:27am
Quads are done with 2 dual gpus = pcie1 @ x8 pcie3 @ x8
3-way = triple at pcie1 @ x8 pcie3 @ x8 pcie5 @ x4

dont know where you get x1 it wont drop that low with all slots populated



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Posted By: ksquared
Date Posted: 16 Aug 2019 at 11:27pm
Originally posted by gizmic gizmic wrote:

Quads are done with 2 dual gpus = pcie1 @ x8 pcie3 @ x8
...
dont know where you get x1 it wont drop that low with all slots populated



OK, now I understand much better. My definition of "all slots" included PCIE2 or PCIE4, since I was thinking there would have to be four graphics cards for "quad."



Posted By: foxx1337
Date Posted: 17 Aug 2019 at 4:38am
My Vega56 is plugged into PCI3. This is what hwinfo64 says:


and also 8 GT/s in the Sensor Monitoring window. Looks like PCIe 3 x16 to me.

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Ryzen 3900X, Taichi X570


Posted By: Ray62
Date Posted: 17 Aug 2019 at 2:11pm
Pay attention! This is just an information for the capabilities of the card.
You should check the PCIE slots under Motherboard->SMBIOS DMI->System Slots where you can see the slot data bus width. The PCIE3 will show you the 8x mode, i guess.

-------------
Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: shmerl
Date Posted: 19 Aug 2019 at 2:45am
Or on Linux, try lstopo.


Posted By: foxx1337
Date Posted: 19 Aug 2019 at 4:08am
Hey Ray62, I didn't know about that. I don't think it does, instead:





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Ryzen 3900X, Taichi X570


Posted By: gizmic
Date Posted: 19 Aug 2019 at 10:26am
Originally posted by foxx1337 foxx1337 wrote:

My Vega56 is plugged into PCI3. This is what hwinfo64 says:


and also 8 GT/s in the Sensor Monitoring window. Looks like PCIe 3 x16 to me.



pcie3 X16 = pcie4 X8 (8GB/s)

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Posted By: Ray62
Date Posted: 19 Aug 2019 at 3:48pm
Originally posted by foxx1337 foxx1337 wrote:

Hey Ray62, I didn't know about that. I don't think it does, instead:





It looks as it should in the PCIE3 slot:
GPU is a PCIe 3.0 one
Max. link width is 16
Current link width is 8

If you would place the card in PCIE1, it should be:
GPU is a PCIe 3.0 one
Max. link width is 16
Current link width is 16

-------------
Asrock Fatal1ty X370 Professional Gaming Offline
Under test:
MSI X570_MEG_ACE | AMD Ryzen 9 3900X | Scythe Mugen5 | 2x16GB F4-3200C14D-32GTZ@3466 | ASUS GeForce GTX 1080 Ti FE


Posted By: foxx1337
Date Posted: 20 Aug 2019 at 7:02am
You're wrong, Ray62; according to https://en.wikipedia.org/wiki/PCI_Express#History_and_revisions, PCIe 3 works at 8 billion transactions per second.

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Ryzen 3900X, Taichi X570


Posted By: gizmic
Date Posted: 20 Aug 2019 at 10:18am
thats the transfer rate / link rate it doesn't change in the whole pcie3 range x1-x16

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Posted By: shmerl
Date Posted: 06 Sep 2019 at 9:26am
OK, I run a test (The Witcher 3 in Wine+dxvk on Linux, 1920x1200, max settings, hairworks off). I don't see any difference in framerate, besides regular fluctuations:

slot 1:


slot 2:


So I'd assume the difference is slots not impacting it.


Posted By: gizmic
Date Posted: 06 Sep 2019 at 3:42pm
even if its a titan or a dual pcie3.0 8X is more than enough

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Posted By: Xaltar
Date Posted: 06 Sep 2019 at 4:03pm
Originally posted by gizmic gizmic wrote:

even if its a titan or a dual pcie3.0 8X is more than enough


Agreed, currently I don't believe even the 2080ti or RTX Titan can fully saturate
the bandwidth of PCIe 3.0 x8. As far as I am aware, they can barely saturate
PCIe 3.0 x4. Contrary to popular belief, GPUs do not fuel PCIe development, it is
mostly designed for storage and network throughput. GPUs are quite a bit behind
what a PCIe SSD or high bandwidth LAN adapter can demand.

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