AMD Zen 4 & Socket AM5 Explained: PCIe Lanes, Chipsets, Connectivity

[Bomby569]

Is it really necessary to give consumer boards 16x lanes of PCI 5.0?
I thought that video cards doesn't even use full 16x 4.0 lanes.

This thought came in my mind thinking that maybe they could use the spare lanes for other purpose. Or maybe couldnt' they check if the device connected has 8 or 16 lanes and dedicate the spare lanes for other connections?

I clearly am talking from a point of view of a ignorant in this matter

I have no idea why they did it, but there's those pcie cards for multiple m.2 support. Not everything that goes into PCIe is a gpu.

 

[chrcoluk]

That Asrock solution is pretty neat but AMD is pushing for mandatory gen5 on the m.2 slot on both x670 and b650 to offer an incentive for storage vendors to also bring those solutions to market quickly. The advantages are not really visibly right now but I think the hope is with direct storage they'll be able to offer some major performance advantage quite soon.

To the cost point, Moore's Law Is Dead is reporting that 2 X670 chipsets are cheaper than a single X570, if true that already goes some way towards absorving the price increase from moving to pcie gen5 and extra layer pcbs.

The argument of "what gamer needs pcie gen5" is also completely flawed, you could also say "what gamer needs a new gen system when the last gen is selling at a discount" or the classic "what gamer needs more than 4 cores". Software that makes use of higher speeds/performance will be available as higher speeds/performance becomes available, not the other way around. Granted we haven't really scratched the surface of what gen4 nvme is able to do because it was also a short lived spec, but that doesn't mean we can't continue to move forward on the hardware side while the software catches up.

Yes the argument is not limited to pcie5, but its a much stronger argument, its really only there for nvme, and directstorage will probably be just fine on gen3. Far from completely flawed, also by the time directstorage is a thing worth worrying about these boards wont be in production anymore. Here and now matters.

Based on your comments here, did you even read and understand my article?


Six it seems, as only DDR4 Intel boards use four layer PCBs from what I've seen. PCIe 5.0 seems to require eight if there's a x16 slot, but can do six if it's only for the M.2.

yes considering my comments are based on it, feel free to correct what you think I misunderstood.

How many layers does DDR5 require? And other things, like the quality of insulator between layers? If the requirements for PCB for DDR5 are as strict as they are for PCIe 5 then the latter can't increase the price much.

Yes but I did say DDR4 as well since thats cheaper to buy and tied in with gen3 means cheaper boards.

Most extra performance on AM5 will come from the new CPUs the rest is expensive iceing on the cake. Intel DDR4 boards have shown this.

 

[TheLostSwede]

yes considering my comments are based on it, feel free to correct what you think I misunderstood.

First of all, routing the CPU lanes to slots would add a lot of cost, as it would require a more advanced PCB layout, PCB and PCIe 5.0 redrivers.
Not impossible, but expensive.

The market trend, for better or worse, is towards more M.2. However, the board layout is based on what the motherboard makers cook up, so if you have an issue, it's them, not AMD's fault.

The chipset has four lanes because of cost. More lanes equals bigger chip, which equals more cost in every single step of the manufacturing process.
Yes, Intel moved to eight, for some of its chipsets. AMD chose a different route, but can clearly move to PCIe 5.0 for the next generation.

PCIe 3.0 is clearly not dead, since each chipset can support four lanes and/or SATA. I guess you didn't read the Gigabyte board news post from Computex, but they use PCIe 3.0 for Ethernet and WiFi.

The B650 boards will be a lot cheaper and if you'd read any of the news posts about upcoming motherboards, you would've known there will be more affordable X670 boards too.
However, PCIe 3.0 will end up being a peripheral interface only moving forward, so get used to it.

So many people seem to misunderstand how PCIe works as well and this isn't directed at you as such, but it's not possible to take eight lanes of PCIe 5.0 and magically make it into 16 lanes of PCIe 4.0, it requires expensive ICs, as PCIe wasn't designed to work in that way. This is why we're getting PCIe 5.0 x16 slots, since if you plonk a PCIe 3.0 graphics card in there, it will end up running at 16 lanes of PCIe 3.0 bandwidth, not four lanes of PCIe 5.0. It would be great if someone could conjure up a cheap chip that would allow this, but sadly, there's no such thing.

85-90% of people never put an add-in card in their computer these days outside of a graphics card. We're a minority, so the motherboard makers are catering to the YouTubers who clearly are going banans for M.2 right now. Maybe go complain to them and things will change, if they change their tunes. (Yes, you pointed this out).
Also, most motherboards come with WiFi and Bluetooth built in these days, so no-one's going to add that.
Most video capture, unless it's for professional use, is USB based these days.

M.2 slots are a lot cheaper in production, as they're added during SMT, whereas through-hole components are added by hand, usually by underpaid workers from the Philippines if the boards are made in Taiwan, or equally underpaid workers from the xinese countryside if the boards are made in xina. Each manual step has a higher cost than something that can be done by a machine. You're confusing market segmentation with actual cost.

This is a bit old now, but I've been to this specific factory some years ago. A bit past the 5:40 mark is where the through hole components are being added, by hand.

 

[chrcoluk]

Thank you for the high effort reply Swede is it is appreciated.

I have deleted my full reply as I felt I didnt want to be argumentative now on this, but I will edit it back in if you want me to.

 

[Mussels]

Yes the argument is not limited to pcie5, but its a much stronger argument, its really only there for nvme, and directstorage will probably be just fine on gen3. Far from completely flawed, also by the time directstorage is a thing worth worrying about these boards wont be in production anymore. Here and now matters.

Have you not seen that AM4 x370 boards are still valid and supported

AM5 is going to be more expensive than the still for sale AM4, so they're making sure theres actual upgrades to the platform as opposed to how a competing platform does things (cough 10th gen to 11th gen)

With multiple generations of CPU's and motherboards being compatible, it makes sense to start with PCI-E 5 to the essentials from the very beginning, with each generation adding it to more of the board as costs decrease (and incentive to upgrade, for those who need it)

There is no reason B650/x670 wont be on sale for 2-3 years, i can still buy B450 boards new to this day and they have support for CPU's launched years after they did.

 

[Chrispy_]

Is it possible to bifurcate one of the sets of PCIe 5.0 x4 general purpose lanes, or is that something only the chipset can do?

I'd rather see more M.2 drives. A pair of PCIe 5.0 SSDs isn't as likely as a single PCIe 5.0 SSD and then a whole bunch of slower PCIe 3.0 drives.

I'd have more than two drives in my B550 machine if it had more M.2 slots, but two is often all you get given.

 

[trsttte]

Is it possible to bifurcate one of the sets of PCIe 5.0 x4 general purpose lanes, or is that something only the chipset can do?

I'd rather see more M.2 drives. A pair of PCIe 5.0 SSDs isn't as likely as a single PCIe 5.0 SSD and then a whole bunch of slower PCIe 3.0 drives.

I'd have more than two drives in my B550 machine if it had more M.2 slots, but two is often all you get given.

You want to take one pcie5.0 x4 to multiple pcie4.0/3.0 2x or even 4x? You'd need a pcie switch aka PLX chip, or the chipset (thought the way they work is different I think, the chipset just bottlenecks stuff, a plx switch gives you full access to the capabilities according to the division implemented).

4 m.2 slots is getting more popular, several of the X570S (the "silent" passive cooled refresh) had 3 or 4 (1 cpu, 2 or 3 from chipset), from the next gen x670e boards that were previewed several were also using 4 m.2 slots (2 from cpu + 2 from chipset).

 

[Mussels]

Is it possible to bifurcate one of the sets of PCIe 5.0 x4 general purpose lanes, or is that something only the chipset can do?

I'd rather see more M.2 drives. A pair of PCIe 5.0 SSDs isn't as likely as a single PCIe 5.0 SSD and then a whole bunch of slower PCIe 3.0 drives.

I'd have more than two drives in my B550 machine if it had more M.2 slots, but two is often all you get given.

That'd be a chipset thing and it's already happened in previous gens. x370 went from 3.0 to 2.0 slots, B550 goes from 4.0 to 3.0 slots, etc.

It's why i think they needed the 5.0 this early, to give them the freedom of bandwidth for all the hungry accesories hanging off the chipset (40Gb USB 4.0, 10Gb NIC's, wifi 6E, NVME etc)

 

[Flaky]

Is it possible to bifurcate one of the sets of PCIe 5.0 x4 general purpose lanes, or is that something only the chipset can do?

It may be hard to get concrete data. At least AM4 was capable of that, with x4 storage link being able to split into multiple x1 with option of turning two of those lanes into SATA.

 

[mahirzukic2]

Seen title and only thing that came to mind was


The foot bone’s connected to the leg bone.
The leg bone’s connected to the knee bone.
The knee bone’s connected to the thigh bone.
…….

edit. Can I get a pci slot to use my old school sound card??

Sure you can. Using one of these converter cards.

 

[Mussels]

Jesus this makes my head hurt

 

[Butrus]

I think AMD made a mistake with only providing 28 PCIE lanes on AM5.

AMD would be mad if the AM5 hasn't place for more than 28 lanes. I'm very confident that the AM5 will allow for at least 32 lanes PCIe (probably even gen6 in the future), my bet would be that there are pins ready for at least 40 lanes. It all depends what Intel will bring with Raptor Lake, Meteor Lake and later on...

Remember that Raphael != AM5 socket...

Is it possible to bifurcate one of the sets of PCIe 5.0 x4 general purpose lanes, or is that something only the chipset can do?

That's a very good question. I think the CPU itself will probably allow for a sub x4 bifurcation on some of the lanes but if so it will be rarely enabled in the BIOS. Remember that those things are managed from the chipset via one of the management interfaces (like I2C) and it is usually being set in the BIOS.