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PCIe 4.0 May Come to all AMD Socket AM4 Motherboards

mikewinddale

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Dec 22, 2016
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I'd like to know how many PCIe 3.0 lanes Ryzen 3xxx will have. It's kind of depressing when your motherboard tells you that the second M.2 is only PCIe 2.0, and that installing a second M.2 disables one of the PCIe slots. I'd like to have enough PCIe 3.0 lanes to fill up all my M.2 and PCIe slots. Or at least enough that filling one slot doesn't entirely disable another.
 
Jan 9, 2019
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6th Paragraph down "Our sources tell us that AMD can simply lock out that feature and that the fate of PCIe 4.0 support on 200- and 300-series motherboards haven't been communicated to them yet" Should be "300- and 400-" instead of "200- and 300-"
 

LinuxDevice

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May 20, 2017
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Right now even the fastest video card isn't bottlenecked on PCIe v3. I suspect it will be a long time before anything "consumer" uses PCIe v4. However, there's a new generation of 100Gb/s networking that might suddenly have meaning (and perhaps controllers of massive storage warehouses).

Someone else asked a question about how many lanes though...I imagine that if suddenly a video card works with PCIe v4 and runs at full speed even with x4 or x8 it'll free up lanes for other uses.
 

jimmysmitty

Polypheme
Moderator


I will assume same as before, 16 lanes and 4 for M.2 NVMe drives with any others being fed by the chipset, possibly the chipset will be upgraded to PCIe 3.0 or I hope as thats one advantage Intel has had.



By the time we would benefit from PCIe 4.0 AM4 will be a dead socket.
 

none12345

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Apr 27, 2013
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Not needed, but cool if true. Ill take a free upgrade to pci4! No need to buy a new mobo if true, tho ill probably still buy one to replace another old system.

Looking at that 8 core vs 9900k demo...cant wait for a 12 core zen2 chip. I dont really need it, i just want it. At least i want a 12 core ~4.7+ ghz chip.
 

hannibal

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Apr 1, 2004
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Does the amd need 12 to 16 cores now? They can definitely do it, but is there any economical reason for that at this moment? Maybe normal 8 core versions 2019 and two cpu 16 core version at 2020, when 7nm is cheaper to produce? They already have Intel in trouble at this moment.
Also how hard it would be make old chipsets compatible with 16 core Ryzen 3000? I am sure that x570 could make it, but can older 300 and 400 series? There Are Many interesting thing to find out.
We can be sure that we see 16 cores at least in am5 processor socket or what ever comes after am4. But Until that there Are some backward compatibility issues that has to be maintained. Maybe it is possible maybe not. We don`t know yet.
 
Thanks for the well tempered article. Finally, a good mix of crystal ball and good sense that doesn't conflict so much with reality, while actually bringing a welcome message.

Maybe it's wishful thinking, but I was certainly hoping that at least some limited PCIe 4 functionality would make it's way to at least some of the currently existing crop of AM4 motherboards. While there's no guarantee, it's encouraging that I'm not the only one having similar thoughts in this regard.

Folks tend to forget that, while nothing may need the extra ability provided by PCIe Gen 4, having more resources available for a PC's disposal isn't going to hurt anything, and usually results in a smoother, cooler, less bogged machine under heavily loaded situations, or in the case of peripheral buses, allows other devices access to resources more often, as the bus can be freed up sooner for use by other devices.

It may seem wasteful to be unable to fully utilize the newer bus speeds, but as we've seen in the past, such as when the first UDMA hard drives hit the market, there were quality of life style improvements as the overhead for using the hard disk started to diminish, resulting in what can only be described as a smoother operation of the overall system.
 

Olle P

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Apr 7, 2010
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Nice for us early adopters if true, but it will take a while Before i get any attached device that can make use of PCIe 4 anyway. (Just like I have very few USB3 devices but many USB2.)

If you by "this moment" mean "more than half a year from now" and there then will be a market for it: Yes!

 

InvalidError

Titan
Moderator

Changing the number of CPU-hosted PCIe lanes would most likely require a new socket and definitely require a new motherboard to re-route whatever pins get re-purposed for those if it was done on AM4, so don't expect the number of PCIe lanes to change until AM5 or whatever AMD's next socket ends up being called.
 

shmoochie

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May 10, 2018
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Given that video cards nowadays aren't bottlenecked by pcie 3.0, could they restrict a slot to using 8 lanes of pcie 4.0, leaving the extra 8 open for m.2 or whatever else?
 

drinking12many

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Apr 8, 2011
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As always more cores faster video encoding. I don't need a threadripper, but more faster cores on AM4 sounds good to me as always price is the biggest factor.
 

dave_trimble

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Jul 3, 2013
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I'm still running a Haswell 4790K, which has been plenty for my gaming needs until recently, now that Shadow of the Tomb Raider maxes it out at 100% across all cores and threads while also 100% on my 1080ti.

I think Ryzen 3000 series will be my first platform upgrade since 2015. Glad I waited. (I will, of course, be waiting for reviews to come out before I take the plunge)
 

InvalidError

Titan
Moderator

While AMD's CPUs support splitting the CPU PCIe host into multiple ports, implementing that flexibility on the motherboard requires a bunch of PCIe muxes, which means more parts, more cost and more power, so most motherboard manufacturers don't bother with those in the mainstream beyond the usual x16x0/x8x8 for SLI/CF on such motherboards. PCIe 4.0 being newer, PCIe 4.0 versions of said switches and related support circuitry is going to be significantly more expensive until the 3.0 stuff gets deprecated.

As long as the chipset link gets upgraded to PCIe 4.0 to alleviate the CPU-chipset bottleneck, running NVMe SSDs off chipset lanes will be perfectly fine for 99.99% of normal people. The SATA to NVMe upgrade is already marginal for many, 3.0x4 to 4.0x4 is going to be imperceptible to most under typical everyday use, so there is no point in motherboard manufacturers wasting effort on accommodating that in mainstream boards.

If you insist on having your NVMe SSDs on CPU-hosted lanes and can't find a motherboard you like that supports it, you can always get an SLI/CF motherboard and use an NVMe adapter in the second GPU slot.
 

shmoochie

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May 10, 2018
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Ah that makes sense. Thank you for the informative response. I had just wondered if halving the number of pcie lanes dedicated to each slot would be a viable solution for future mobos, but I see that it isn't cost effective at least right now. I'm sure manufacturers would also prefer we keep the same number of pcie lanes so that they can have headroom for upgrades.
 
Jul 12, 2018
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In my experience few if any motherboard makers will update anything other than their newest boards and if we are lucky, one or two versions back. But older boards seem to be forgotten and we are left to pay out for a new board to get updates.
 
"I'd like to know how many PCIe 3.0 lanes Ryzen 3xxx will have. It's kind of depressing when your motherboard tells you that the second M.2 is only PCIe 2.0, and that installing a second M.2 disables one of the PCIe slots. I'd like to have enough PCIe 3.0 lanes to fill up all my M.2 and PCIe slots. Or at least enough that filling one slot doesn't entirely disable another."

Well, the PCIe M.2 connectors should use the CPU's (not chipsets) lanes so Zen2 should help, but what happens if people enable PCIe v4.0 after a BIOS flash? That will eat up some PCIe lanes that the CPU had so that option may make all M.2 functionality disabled on some boards?

(That's why I think AMD's making a bad decision. Nice to have the options though the confusion may cause a lot of issues)

*I believe Zen currently has 24 PCIe lanes?
My guess is that Zen2 (3000 series) will have between 40 and 64 lanes. If it has 40 lanes then you could in theory, after BIOS flash, have PCIe v4.0 for the top card and everything else should stay the same.

**Again don't forget that a newer CHIPSET adds additional lanes too. The CPU matters most for the top graphics card and M.2 functionality. A better chipset for example should be used for SATA completely and leave M.2 alone on the CPU so this either/or issue doesn't happen.

I think they should commit to 64 (PCIe v3.0) lanes (same as Threadripper) if possible so you could have x16 PCIe v4.0 and x28 PCIe v3.0.

A BIOS flash even still though might not make all M.2 and SATA work at the same time on current motherboards. No idea as I'm not clear on how that's wired up. Just having more bandwidth doesn't mean you can use it... if it's a JUMPER for example that's probably physically disabling copper traces so there's no way software/firmware updates help.
 
My MATH was wrong above but I can't edit... if there were 64, PCIe v3.0 lanes then it should work out to x16 PCIe v4.0 (x32 PCIe v3.0 bandwidth) and another x32 PCIe v3.0 lanes.

I'm not saying the current motherboards would support that after a BIOS flash (probably will vary), and again I'm suspecting at minimum Zen2/3000 will have 40 PCIe v3.0 lanes but my hard money is on 64 same as Threadripper (which I believe is x32 PCIe v4.0).
 

InvalidError

Titan
Moderator

I seriously doubt AMD can change the number of CPU PCIe lanes without introducing a new socket as this would require re-assigning pins and possibly breaking socket compatibility. When was the last time that a CPU had major integrated IO changes (adding 16 PCIe lanes would spell 64 pins re-purposed for IO signals along with 30+ pins re-purposed for PCIe IO power, so we're likely talking about re-defining 100+ pins) without a new socket? I can't think of any. And with Ryzen 3000's multi-chip construction, it may very well need all the power and ground pins it can get to support those 12+ cores or high-end APUs.

Ryzen 3000 will most likely have the exact same x16/x8x8/x8x4x4 main PCIe controller, x4 for chipset and x4 for NVMe/USB3.1-gen1/2 as Ryzen 1000 and 2000. Most new, updated and extra IOs will have to come from the 500-series chipsets, which is fine as long as the chipset link is fast enough not to be a meaningful bottleneck in typical use. (If it is for you, then you may need to go TR4 or EPYC.)
 

s1mon7

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Oct 3, 2018
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I don't think that matters for builders. If I were to build a Ryzen system, it would outlive many generations of GPUs. People replace mobos every 6-7 years on average. The fact no new CPUs will be out for AM4 in 2-4 years isn't important if the fastest AM4 CPUs are still fast enough for most peoples' needs at that time. The fact they will be able to pop in the newest GPU or SSD and it'll work at full speed is great and they will be able to fully take advantage of and appreciate this feature for many years to come.
Think of it this way - if you bought a Ryzen board in 2017, you can upgrade to the fastest Ryzen chip in 2020 and use PCIe 4.0 devices for years to come after that, without worrying your mobo will limit a GPU you buy in 2022 or 2023. That's some great life for a 2017 board that suddenly got PCIe 4.0 support nobody even expected when they were buying their board.

Whenever I read such stories from AMD I grow more and more respect for them.. and envy, since I'm on an Intel system that launched the year Ryzen did and was outdated the very same year with 0 support now. If this story was about Intel, they'd just prevent OEMs from enabling such feature on older boards and require a new chipset, even if implementing it was entirely feasible on older boards (just sayin').
 
I also agree the amount of PCIE lanes will not change as those are tied to the pins on the socket. Of course you will have double the bandwidth on PCIE 4.0 so its like 48 lanes of PCIE 3.0 in bandwidth. That should be more than enough for 90% of the cases.

As an original Ryzen owner Im almost certainly going to be upgrading to Ryzen third generation. I'm still holding onto my GTX 1070 from fall of 2016 so getting a new GPU when Navi or Nvidia's 7nm is released should be perfect timing to take advantage of PCIE 4.0.
 

jimmysmitty

Polypheme
Moderator


My point is that by the time PCIe 4.0 is a needed option AM4 will be long gone and most builders will have moved on. PCIe 3.0 is still very viable for builders. Now for HPC and server class PCIe 4.0 will be very welcome as they can and do use all the bandwidth available from every part.

One thing though it will depend on the manufacture. I can say I have a few ideas of brands that will push BIOS updates to support it but I may be surprised.



Doubling the bandwidth would put a 16 lane PCIe 4.0 the same as 32 lanes of PCIe 3.0.

And remember per the article its the first PCIe slot that will be able to run 4.0 as the rest will be too far out. I do wonder if it will affect the M.2 slots as they tend to be below the first PCIe x16 slot.
 

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