AMD x570 chipset pci-e lanes

[tropox]

hi all, two quick questions
1)
many x570 motherboards (for example MSI MPG x570 Gaming Edge Wifi) list the chipset M.2 slot as 3.0 x4
now i know that the x570 chipset should have a total of 4.0 x4
so i suppose that the chipset M.2 slot has 4.0 x2 and they just write it as 3.0 x4?
what makes me unsure is that i remember that in most previous generation motherboards, the chipset M.2 utilizes the full chipset bandwidth and that in previous generations the total chipset lanes were one generation lower (2.0 x4 for example) than the cpu lanes as well
so it makes me wonder if the M.2 slot does utilize the full chipset bandwidth but that is not 4.0 x4 but 3.0 x4
im just a bit confused by the way its written and because of (2)

2)
the Asus Pro WS X570-ACE specifications mention:
pci-e slots:
- chipset: 1 x PCI Express 4.0 x 16 slots (max. at x8 mode)
how the hell is it possible for the chipset pci-e slot to be 4.0 x8 (we are not talking about the physical dimensions which is x16 but the bandwidth which is clearly listed as x8) when the chipset is 4.0 x4?
it doesnt add up and this is what made me wonder about the M.2 slots bandwidth as well

thank you very

 

[Jandor]

Because you get the PCIe 4.0 x8 from dividing the lanes from PCIe 16 4.0 x16 from the CPU when the second slot is used. So when both slots are used, they both become PCIE 4.0 x8 (which is equal to one PCIe 3.0 x16) which is very much enough by today standards. In that case, you may eventually get some enhanced performance from a RX 5700/XT compared to all equivalent cards, especially Nvidia who will run on PCIe 3.0 x8 (which is already fairly enough)

 

[tropox]

Because you get the PCIe 4.0 x8 from dividing the lanes from PCIe 16 4.0 x16 from the CPU when the second slot is used. So when both slots are used, they both become PCIE 4.0 x8 (which is equal to one PCIe 3.0 x16) which is very much enough by today standards. In that case, you may eventually get some enhanced performance from a RX 5700/XT compared to all equivalent cards, especially Nvidia who will run on PCIe 3.0 x8 (which is already fairly enough)

(this is about question 2)
jandor, once again:
- CHIPSET: 1 x PCI Express 4.0 x 16 slots (max. at x8 mode)
thats a chipset pci-e 4.0 x16 (x8) not a cpu pci-e 4.0 x16 (x16 - dual x8)
so how is that possible? the chipset's total bandwidth should be 4.0 x4

 

[owcraftsman]

In the case of the MSI MPG x570 Gaming Edge there is only one PCIe 4.0 x4 M.2 slot (M2_1) the other M.2 is PCIE 3.0 x4 (M2_2) (source: Manual pg 16)
Conversly the MEG x570 ACE has 3x-PCIe 4.0 x4 M.2 (M2_1, M2_2, & M2_3) 1-from CPU and 2 from chipset but that comes at a cost.
Although I'm not certain what that is but I'd say at least 2 if not 4 of the Sata Ports would be disabled if all 3 M.2 slots are populated unless the SATA Ports are controlled by an Asmedia chip.
Bottom line do your research before buying your mobo.
Source http://download.msi.com/archive/mnu_exe/mb/E7C37v1.1.pdf

 

[sirmonkey1985]

i feel like the original poster is confusing the bandwidth between the cpu and the chipset and the additional pcie lanes from the chipset.. yes the pcie lanes from the cpu to chipset is 4 lanes.. either pcie 3.0 x4 or pcie 4.0 x4 depending on the CPU.. from there the chipset has it's own additional lane options as shown in the images above but that also doesn't mean the motherboard manufactures have to abide by that. they can modify certain parts of it, e.g. asrock runs 8 sata ports and instead of disabling 2 of them for the second m.2 off the chipset they disable the bottom pcie x4 slot when that m.2 slot is used.. ultimately you're still bottlenecked by the 4 lanes between the cpu and chipset.


as far as the asus professional board it runs in x16/x0 or x8/x8 off the cpu with a 3rd pcie 4.0 x8 slot off the chipset because they figure the user is more likely to do computational/accelerated gpu workloads and would be more likely to run multiple gpu's. this is also why it's one of the few x570 boards to run a u.2 slot off the chipset along with a second m.2.

 

[tropox]

thank you for the replies

In the case of the MSI MPG x570 Gaming Edge there is only one PCIe 4.0 x4 M.2 slot (M2_1) the other M.2 is PCIE 3.0 x4 (M2_2) (source: Manual pg 16)

i really dont see your point, i wrote the same thing in my first post, here:

the chipset M.2 slot as 3.0 x4

also i know there are exceptions like the other motherboard you mentioned
-

i feel like the original poster ...
as far as the asus professional board it runs in x16/x0 or x8/x8 off the cpu with a 3rd pcie 4.0 x8 slot off the chipset because they figure the user is more likely to do computational/accelerated gpu workloads and would be more likely to run multiple gpu's. this is also why it's one of the few x570 boards to run a u.2 slot off the chipset along with a second m.2.

like you said, the total bandwidth of the chipset lanes is 4.0 x4 pci-e lanes
if you add the maximum bandwidth of each "additional" pci-e lane from the chipset though, you get a higher number
how is that possible? its not possible because they are not additional pci-e
they are pci-e lanes split from the chipset, they just share the bandwidth, they dont add up
the reason is simple, they dont work constantly and they dont work all together so they share it
and if they try to work all together then they get bottlenecked just like you said
ok so far?

the Asus board mentions a chipset pci-e 4.0 x16 (x8) slot
the x8 is not the result of adding up the maximum bandwidth (every x4) of multiple slots/devices that share the same x4 bandwidth
the x8 is about a single slot/device, they say that slot, that device has a bandwidth of x8 4.0 pci-e lanes
so they are saying that a slot coming from the chipset (which has a total bandwidth of 4.0 x4) supports more bandwidth (4.0 x8) than the chipset itself
where is my confusion?

 

[owcraftsman]

hi all, two quick questions
1)
many x570 motherboards (for example MSI MPG x570 Gaming Edge Wifi) list the chipset M.2 slot as 3.0 x4
now i know that the x570 chipset should have a total of 4.0 x4
so i suppose that the chipset M.2 slot has 4.0 x2 and they just write it as 3.0 x4?
what makes me unsure is that i remember that in most previous generation motherboards, the chipset M.2 utilizes the full chipset bandwidth and that in previous generations the total chipset lanes were one generation lower (2.0 x4 for example) than the cpu lanes as well
so it makes me wonder if the M.2 slot does utilize the full chipset bandwidth but that is not 4.0 x4 but 3.0 x4
im just a bit confused by the way its written and because of (2)

2)
the Asus Pro WS X570-ACE specifications mention:
pci-e slots:
- chipset: 1 x PCI Express 4.0 x 16 slots (max. at x8 mode)
how the hell is it possible for the chipset pci-e slot to be 4.0 x8 (we are not talking about the physical dimensions which is x16 but the bandwidth which is clearly listed as x8) when the chipset is 4.0 x4?
it doesnt add up and this is what made me wonder about the M.2 slots bandwidth as well

thank you very

I tried to answer both questions succinctly sorry for the confusion.
#1 Configurations vary by motherboard (see top slide I posted center bottom)
#2 I pointed you towards a manual for one of the motherbords mentioned and suggeted you do the same to get your answers on a per board basis.
#3 I pointed out a clear difference between two different motherboards to illustrate how different they can be.
#4 Every X570 chipset motherboard with a 3rd Gen Ryzen has 24 High-Speed Lanes available-PEROID, but depends on #1
#5 Every X570 Chipset has 16 High-Speed Lanes 12 Flexible Gen 4 Lanes and 4 coming from the the CPU downlink (again seel slides posted)
#6 2nd Gen Ryzen is compatible with the X570 Chipset but no Gen 4 Lanes are available which can be a source for confusion.
#7 4.0 x8 can only be assigned to graphics. You may be confused by 2x4 to M.2 which is not x8 even though it would be using 8 Lanes
#8 Your question may not be specific enough to formulate the answer you are looking for. If you could tell us what you want to accomplish maybe that would help.
If your goal here was to point out it's confusing we agree but there is a logical answer otherwise.

ASUS Pro WS X570-ACE specifications; Storage:
3rd Gen AMD Ryzen™ Processors - 1 x M.2_1 socket 3 with M Key, Type 2242/2260/2280/22110
(PCIE 4.0 x 4 and SATA modes) storage devices support
2nd Gen AMD Ryzen™ / 2nd and 1st Gen AMD Ryzen™ with Radeon™ Vega Graphics Processors
- 1 x M.2_1 socket 3 with M Key, Type 2242/2260/2280/22110
(PCIE 3.0 x 4 and SATA modes) storage devices support
AMD X570 chipset - M.2_2 socket 3* with M Key, Type 2242/2260/2280
(PCIE 4.0 x 2) storage devices support
- 4 x Serial ATA 6.0 Gb/s connectors with RAID 0, RAID 1 and RAID 10 support
- 1 x U.2 connector (supports U.2 NVMe device)
* The M.2_2 socket shares PCIe lanes with PCIeX1_1; when PCIeX1_1 is occupied, M.2_2 only can only run at PCIE 4.0 x 1.

As mentioned above different configuration come at a cost for example with the Pro WS The M.2_2 socket shares PCIe lanes
with PCIeX1_1; when PCIeX1_1 is occupied, M.2_2 only can only run at PCIE 4.0 x 1

The WS is one of few that can do 3-way CF at 8x8x8 but this config comes at a cost too. (see #4 Above)

Source: https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/Pro_WS_X570-ACE/E15611_Pro_WS_X570-ACE_UM_V2_WEB.pdf (pg vii & 1-8)

 

[tropox]

I tried to answer both questions succinctly sorry for the confusion.

The WS is one of few that can do 3-way CF at 8x8x8 but this config comes at a cost too. (see #4 Above)

friend, take a break and see what the questions are and what your answers are
im asking questions about the specifications and your answer is to keep repeating the specifications
so let me be clear, i do have read the specifications of both the motherboards i have mentioned, because that is where my questions come from in the first place
i couldnt have questions on the specifications unless i had read them first
what you are doing is to send me back to the specifications and find my questions again, do you understand or not?

again, the easy one, number 2, the specifications say (10th time they are written down):
chipset pci-e slot 4.0 x16 (x8)
how could i be asking what the specifications are, when i have already wrote them in the first post?
im not asking what the specifications are
your answers is yet again, what the specifications are

the question is HOW is it possible to have a single chipset pci-e 4.0 x16 (x8) with 4.0 x8 bandwidth when the total bandwidth of the chipset (where the slots pci-e come from) is less than that (4.0 x4)
let me quote your answer:

The WS is one of few that can do 3-way CF at 8x8x8 but this config comes at a cost too

im asking how it is possible to be x8 and your answer is "it is x8, it says that on the manual"

 

[sethk]

The chipset is switching the lanes. Maximum bandwidth to the CPU is limited to 4.0 x 4 at any given time through the chipset.

 

[Mikavelli]

YASSS, I found it!
Thank you tropox for motherboard number, and sorry for digging out old thread.

Now pure, practical explanation why exactly someone would use this motherboard.
It's exactly what some video applications need.
I for example have spent already two days looking for some motherboard with 3 x16 slots, with at least x8 physical lanes in each of those.

Those extra lanes, while effectively not used properly if you'll plug in PCIe 4.0 x8 card in PCIe 4.0 slot managed by chipset (due to communication bottleneck between chipset and CPU, of course), are what some professional cards need right now.
PCIe 4.0 cards are barely emerging.

For example, Blackmagic DeckLink 8K Pro, or DeckLink Quad HDMI Recorder, while still made in PCIe 3.0 standard, they REQUIRE 8 physical lanes to send signal.
Mind you, each of those cards can send 4 4K 60fps raw video feeds, in SDI card it's easy to calculate - it's 12G SDI connectors. It means single 4K full quality video feed requires 12Gbps or 1.5GB/s.
Since card has 4 independent ones, it means up to 6GB/s constant throughput in either way. PCIe 3.0 x8 can handle up to ~7.8GB/s - same as PCIe 4.0 x4, by the way.

So, it's a motherboard with layout that makes it possible to use more than one professional video capture card.
1st slot for GPU of course, but 2nd and 3rd thanks to having 8 physical lanes, can support two blackmagic cards.

If you're a gamer, it means you can effectively have 3rd GPU running at PCIe 3 x8, which is enough for now (most GPUs have not filled the x8 throughput yet, but x4 physical lanes would slow them down noticeably)

This is the motherboard I've been looking for, that will allow me to route, mix and switch more than 4 4K sources live.
Now I finally have a finalized PC to buy and build