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ASUS Begins Enabling Limited PCIe Gen 4.0 on AMD 400-series Chipset Motherboards

Oct 4, 2017
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Because your GPU only supports PCIe 3.0 if you were to stick an PCIe 4.0 cappable GPU in it's place then it would probably say PCIe 4.0
That's not how it works you can put a PCIe 2.0 device on a PCIe 3.0 port it wont stop you from enabling PCIe 3.0 on your mobo , same goes here .
Mar 22, 2012
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so.... these MBs have PCIe gen 4.0 support for their m2? is that it?
Aug 20, 2007
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So I guess the NICs, SSDs, RAID cards, etc used for servers are going to be useless and waste of time since according to you PCI-E 4.0 is unnecessary.
*For consumers

In that context, you betcha.

So somehow lower end boards meet the requirements for PCIe 4.0 but the high end ones and ITX don't ? This is total nonsense !
Welcome to the result of using PCIe switches in high end boards.
Dec 30, 2010
746 (0.23/day)
It's not as simple as "flicking a switch" to enable compatibility with a spec which increases data transfer rate by a factor of 2.

This isn't a simple DC wiring problem, it's a time-varying signal which needs to propagate along many transmission lines in the extremely crowded environment of a motherboard PCB. By flipping the switch to double the throughput, you can easily push the circuit outside of it's spec in a number of ways .
- Signal to noise may be violated
- Additional cross talk
- Increased clock jitter
- Disruption of power delivery integrity.

Doubling any switching frequency from a circuit's design spec can break a circuit's capacitive and inductive tuning and completely change the shape of the signal. Anything carrying a current which oscillates in time has the potential to radiate (i.e. becomes an antenna), anything which radiates interacts with and affects its surrounding environment, anything which radiates will be affected by its surrounding environment.

TL : DR - It's not as simple as flipping a switch because electromagnetics are complicated. But also, businesses will be businesses, and only Asus's design engineers would know the exact spec range of their circuitry.

Exactly this ^

But this whole update, even tho my motherboard is in the certified PCI-E 4.0 overview, is useless, since i have a 2700x which does'nt support a native PCI-E 4.0 unless i upgrade the chip obviously.

I'm not touching any bios update at all, since it's working just fine.


New Member
Jun 11, 2019
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I find it funny that the TUF B450 Plus Gaming gets atleast M.2_1 X4 PCIe 4.0 but then the same TUF X470 Plus Gaming doesn't they're practically the same mobo the only difference is the south bridge
If you look closely, there are PCIe switches near the top M.2 slot and 2nd x16 slot of the B450 motherboard, which are absent from the X470 motherboard. That might explain the compatibility differences.
Feb 20, 2019
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This is a nice gesture by Asus for people still using these boards in 5+ years, but right now there aren't any GPUs that benefit from PCIe 4.0 (and it doesn't look like GPUs are going to need any more PCIe bandwidth in the future, either). If the only other thing that gets PCIe 4.0 is a single M.2 slot, then there's not a whole lot of point to this yet.

Currently, speeds of more than 2GB/s for M.2 SSDs are limited to burst mode until the SLC cache is full. Even the best drives drop down to speeds of less than PCIe 3.0 x1 (~900MB/s) once you run out of cache. Sadly, MLC drives are all but nonexistent in the consumer sector and TLC is slowly giving way to QLC as the race to the bottom continues.

Of the two PCIe 4.0 SSD reviews I've seen so far, neither the controller nor the NAND is capable of producing performance that exceeds PCIe 3.0 x4 for anything other than a synthetic burst transfer benchmark; A benchmark that is utterly meaningless because in a real-world scenario such a transfer would be cached in system RAM by the OS anyway and fed to the SSD in the background. Not even 3DXPoint (Optane) can use the bandwidth of PCIe 3.0 yet.

Perhaps in a couple of years from now when SSD controllers have evolved, and if NAND quality hasn't dropped even further from QLC to P(enta)LC or H(ex)LC, we might actually get better transfer rates. Until now, it's just an ePeen race between vendors to claim the highest number on their marketing-departments checkbox feature list.
May 6, 2012
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Jan 31, 2010
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If you look closely, there are PCIe switches near the top M.2 slot and 2nd x16 slot of the B450 motherboard, which are absent from the X470 motherboard. That might explain the compatibility differences.

yeah I saw that and that's what I'd rather have had on the x470 a faster M.2 as I only have an RX580 GPU I don't give a toss about the PCIe 4.0 x16 slot

That's not how it works you can put a PCIe 2.0 device on a PCIe 3.0 port it wont stop you from enabling PCIe 3.0 on your mobo , same goes here .
I would have thought both devices would have to support PCIe 4.0 before it would show up as enabled my GPU is PCIe 3.0 and GPUz only shows PCIe 3.0 at 3.0