PCIe 4.0 on ASUS X470 & B450

[CiBi]

Source: Hexus

 

 

Quote

Strangely the enthusiast X470 boards fare less well than the B450 boards, many of which can use both PCIe Gen 4 add-in cards and PCIe Gen 4 storage

 

Looks like good news for people wanting to save some money on their motherboard. Shame the Crosshair VII doesn't support it through PCIe since that was one of the X470 motherboards I was considering for my Zen2 build.

[LukeSavenije]

but how? the tracing for 4.0 is wildly different

[TVwazhere]

Just now, LukeSavenije said:

but how? the tracing for 4.0 is wildly different

Well.... We do know X570 boards have to have active cooling fans on the chipsets. 

 

Looking at Newegg, The only Asus boards that have the issues are the ones where the chipsets have LED's on the heatsinks.....

 

Coincidence?

[LukeSavenije]

1 minute ago, TVwazhere said:

Coincidence?

not what i meant... it's technically impossible to drive 4.0 through a 3.0 line afaik

[TVwazhere]

1 minute ago, LukeSavenije said:

not what i meant... it's technically impossible to drive 4.0 through a 3.0 line afaik

Quote

The reason for AMD suggesting this. Or pushing for it, is that "There's no guarantee that older motherboards can reliably run the more stringent signalling requirements of Gen 4, and we simply cannot have a mix of 'yes, no, maybe' in the market for all the older motherboards," explained Hallock, adding that "The potential for confusion is too high... the risk is too great."

Sounds like another case of "8th gen Intel cant run on Z270 boards" to me

[CiBi]

Yeah seems to me like its technically possible but depends on signal degradation and such.

 

I also notice that mATX mobo's fair better with 4.0 than ATX and EATX motherboards, might be an issue with the length of the traces?

 

Also Der8auer tested the chipset consumption and if I'm not mistaken the power usage difference between no PCIe 4.0 devices connected and many PCIe 4.0 devices connected is marginal. So there might be another reason that x570 is running hot.

[Jurrunio]

I think it's just some translation failure. The header is in simplified Chinese which is reasonable, but why would the key at the bottom be fully English?

[jdubya421]

Usually traces on boards are designed for either 1. impedance or 2. length (usually both). They probably redesigned the traces so that the PCI signals would all reach at the correct time. Even though they move at "the speed of light" there is still a finite amount of time. Possibly they can overcome this with the controller somehow?

[Jurrunio]

1 minute ago, CiBi said:

I also notice that mATX mobo's fair better with 4.0 than ATX and EATX motherboards, might be an issue with the length of the traces?

Then why the mITX board doesn't support 4.0? That's as short as traces go in the entire lineup.

[LukeSavenije]

4 minutes ago, TVwazhere said:

Sounds like another case of "8th gen Intel cant run on Z270 boards" to me

actually, that one could technically work

 

but ever seen a pcie 2.0 board converting to 3.0 without a plx chip?

[S w a t s o n]

AMD explicitly said that PCIE 4.0 would only be supported on x570 and yet we are finding out that the PCIe 4.0 NVMe drives are achieving the full 5GB/s on PCIe 3.0 boards when you slot in ryzen 3000.

I wonder if lisa is gonna bring the hammer down.
 

 

[The Benjamins]

11 minutes ago, LukeSavenije said:

not what i meant... it's technically impossible to drive 4.0 through a 3.0 line afaik

Thats not true, its just 4.0 signaling is more sensitive so the traces and routing need to be laid out in a way that will have less signal degradation. high quality boards may have traces/routing that support for 4.0 even though it was not originally designed for it.

[LukeSavenije]

3 minutes ago, The Benjamins said:

Thats not true, its just 4.0 signaling is more sensitive so the traces and routing need to be laid out in a way that will have less signal degradation. high quality boards may have traces/routing that support for 4.0 even though it was not originally designed for it.

hm... interesting...

[Trixanity]

43 minutes ago, huilun02 said:

I'm using the X470 Prime and its nice to see free upgrades

Although I'm worried if this will blow up the chipset controller or something

On X570 they needed a fan for cooling?

These would be CPU lanes, not chipset lanes. So it'll be something like only the nearest x16 slot running gen 4 as well as the m.2 slot connected to the CPU. Everything else would be gen 3 including the chipset.

 

That is if this is accurate at all.

[Guest]

Wait I just bought a b450 board before hearing these news. Do other manufacturers also have this pcie 4 compatibility?

[CiBi]

16 minutes ago, Medicate said:

Wait I just bought a b450 board before hearing these news. Do other manufacturers also have this pcie 4 compatibility?

Could be, logic dictates some other boards will be able to use 4.0 as well.

So far only ASUS has published a list with compatibility.

[That Franc]

Hey, not bad, so my B450-I will support the new SSDs then. I haven't expected any Gen4 support, so that's good.

[Drak3]

1 hour ago, TVwazhere said:

Sounds like another case of "8th gen Intel cant run on Z270 boards" to me

Except that AMD's concerns are legitimate.

[mariushm]

Basically it's this:

 

The processor creates some pci-e lanes, which are  pci-e 4.0 with fallback to pci-e 3.0 if signal quality is too bad.

In theory, if the distance between cpu socket and the slots (pci-e x16 and m.2 for SSDs) is short enough and the traces are properly arranged inside the motherboard layers then the signals could be insulated enough and clear enough that a video card or a ssd could run at pci-e 4.0  speeds.

However, on some motherboards it could "borderline".. or it could be that when pc starts and there's just a low amount of "traffic" between cpu and video card there's minimal or no errors, but as you get into a game and a lot of data is being sent to the video card and the video card processor itself and the fans produce a lot of electric noise, then it could be the signal quality through those traces decreases enough that you'd get enough errors to make the processor switch back to pci-e 3.0 speeds. 

Think of it like ethernet cables : you can do 10gbps using a Cat6 cable up to around 40-50 meters, but when you go above this guaranteed length, the quality of the cable is too low and you get too many errors and ethernet card may have to go down to 1 gbps. With cat6a (higher quality cables) you have no problems reaching 10gbps up to 100 meters.

 

So you may or may not get pci-e 4.0 directly between cpu and video card slot and m.2 slot  but the chipset creates pci-e 2.0 lanes still, so the other slots and the extra m.2 connectors would still run at pci-e 2.0

Funny enough, the B450 boards may work better with pci-e 4.0 because you can only have one pci-e x16 slot directly connected to cpu. Splitting the x16 to 2x8 is not possible.

 

The x470 and x370 chipsets allow you to split the first pci-e x16 slot into 2 pci-e x8 slots - this means that the distance between the cpu socket and the second pci-e x8 slot can be long enough for the signal quality to deteriorate enough to no longer work at 4.0 speeds.

[Jito463]

I thought it was already determined that AMD confirmed it could work (and some BIOS versions were shipped with support enabled), but decided to pull any official support because of concerns over confusion, as was referenced in this thread.  I'm pretty sure there was an existing thread on this topic prior to the 3000 series launch.

[ARikozuM]

I see that Asus is a Sony guy. 

 

Spoiler

 

Counter-clockwise on the DS controller.

 

[Master Disaster]

When Asus suggested this didn't AMD come out and say they didn't want this to happen?

 

Also in 99% sure this is a repost. Will have a look now.

[Master Disaster]

Yep, repost...

 

This topic was originally about it being supported but was changed/updated when AMD came out and said they didn't want it to happen.

[Brooksie359]

32 minutes ago, comander said:

The main difference between PCIe 3.0 and 4.0 is signalling rate. 
Loosely speaking, this is "overclocking" the board and its traces. I don't think AMD condones it but if ASUS over-engineered their older boards and it works... all is well. 

I'm going to wait and see how things turn out for this. I am cautiously optimistic about this as a "free upgrade" that I'll likely never use. 

AMD just doesn't want to give it official support. That doesn't mean they are forbidding it or even don't want people to be able to. They likely took this position because they couldn't guarantee the quality and didn't want to say something would work when it only sometimes does. They probably think some will get 400 and 300 series boards assuming that they will still get pcie 4.0 but then realize that it only works with some boards and it isn't the best implementation and then blame it on AMD. 

[Master Disaster]

41 minutes ago, Brooksie359 said:

AMD just doesn't want to give it official support. That doesn't mean they are forbidding it or even don't want people to be able to. They likely took this position because they couldn't guarantee the quality and didn't want to say something would work when it only sometimes does. They probably think some will get 400 and 300 series boards assuming that they will still get pcie 4.0 but then realize that it only works with some boards and it isn't the best implementation and then blame it on AMD. 

And the fact it kind of destroys the idea that X570 needs to be expensive because of PCIe 4 doesn't have anything to do with it at all.

 

Also AMD did forbid it...

Quote

Pre-X570 boards will not support PCIe Gen 4. There's no guarantee that older motherboards can reliably run the more stringent signaling requirements of Gen4, and we simply cannot have a mix of "yes, no, maybe" in the market for all the older motherboards. The potential for confusion is too high. When final BIOSes are released for 3rd Gen Ryzen (AGESA 1000+), Gen4 will not be an option anymore. We wish we could've enabled this backwards, but the risk is too great.

This is the statement from AMDs Ryzen Product Manager. It's pretty definitive, it won't be happening.