Are the two M.2 pcie Gen4 x4 slots on my Zen 4 8845HS Socket FP8 Mini-PC equal?

[eldon_magi]

Hello, quick question, based on the chart below yes, but i would like to confirm, it makes no difference which M.2 slot i install my main OS drive in?
As in intel systems where some lanes are connected to CPU, and other, slower/shared lanes to the PCH. Thanks for any insight.

 

[Wirko]

Does the mini PC's manual mention any differences? Can you test/benchmark the SSD in both slots to see if they perform the same? Do you see any differences in BIOS settings?

 

[dont whant to set it"']

No difference whatsoever between the last ones on the right, same bus speed, same bus width; this is assuming at least one is available, because one could be routed to other controller.
Its a SoC(system on chip) CPU and and PCH are in the same die ,in this case.

 

[eldon_magi]

Does the mini PC's manual mention any differences? Can you test/benchmark the SSD in both slots to see if they perform the same? Do you see any differences in BIOS settings?

Manual mentions nothing, this is one of those cheap chinese mini's, a GMKtec NucBox K8 Plus. I don't think by memory BIOS mentions anything. Below is lstopo output.
Not sure yet if i want to benchmark in both slots, maybe i should.. But final OS will be on ZFS root, so to benchmark i would need to create a temp FS first, and then nvme format before final OS install, not sure yet if i want to do that.

The SN850X is without heatsink, and the 'secondary' M.2 slot sits right under the top fan of the K8 Plus, and it doesn't have the intel AX200 wifi/bt card sitting right under it, so i would rather use that slot.

Not even sure if the 'middle' M.2 slot actually is secondary, i guess it's just some notion ppl have, from the discussions on reddit about this machine..

No difference whatsoever between the last ones on the right, same bus speed, same bus width; this is assuming at least one is available, because one could be routed to other controller.
Its a SoC(system on chip) CPU and and PCH are in the same die ,in this case.

Right, yea one is empty. It sits right above a intel AX200 card, and since the 4TB SN850X is double sided, the middle slot fits better..
I just haven't figured out if it's possible to find out for sure how the pcie lanes are routed on these AMD APU's, so that's why i wanted to ask...

 

[Wirko]

Not even sure if the 'middle' M.2 slot actually is secondary, i guess it's just some notion ppl have, from the discussions on reddit about this machine..

We're talking about the rightmost two ports in the TPU diagram, each of them being PCIe 4.0 x4, right? They should be equivalent, there's nothing to indicate the opposite.

As for benchmarking, even if you already have a filesystem in place and an OS installed, you can still do some tests. Something like copying a few very large files, then many small files, and repeating it a couple times. You'll get some variation because the files are arranged differently each time, and not exactly in the same state of fragmentation etc., but if there were significant differences between the two ports/slots, you'd notice.

 

[eldon_magi]

We're talking about the rightmost two ports in the TPU diagram, each of them being PCIe 4.0 x4, right?

Yes. Both slots are pcie4x4. I was just wondering if any of those pcie lanes are routed to PCH instead of CPU. Typically i would want the main OS drive to be on CPU linked pcie lanes, but i'm not finding any info on how AMD APU's are done regarding this.

I will do KDiskMark benchmarks eventually.. Just looking to format the nvme namespace to 4K LBA sectors, and install an OS on this now..

I earlier played around with another SSD in this system, which was in the other M.2 slot, and it also showed as nvme0n1. So i presume that a single drive will always show up as nvme0. That would allow me to switch the SSD between the M.2 slots without issues booting the OS..

 

[Wirko]

Yes. Both slots are pcie4x4. I was just wondering if any of those pcie lanes are routed to PCH instead of CPU. Typically i would want the main OS drive to be on CPU linked pcie lanes, but i'm not finding any info on how AMD APU's are done regarding this.

Ah, if that's your concern: there is no PCH. The monolithic APU die is all there is.

Compare the diagram you posted to those of the desktop Ryzen 7 8700G, which is almost the same chip. There are multiple diagrams because there are a few chipset options. The upper half of each diagram is the APU - same as yours, with its own ports. The lower half is the chipset, with more ports.

 

[eldon_magi]

Ah, if that's your concern: there is no PCH. The monolithic APU die is all there is.

Yes, sorry if i was vague.. That's exactly what i was wondering. The Ryzen 7 8700G diagrams explain alot, how the APU is linked by pcie4 x4 to the chipset, My APU doesn't have a chipset like the x670 for example at all.

Thanks so much for the help

BTW i really like this machine, paid around 370 EUR barebone.. I think the features are great for that price, starting with 2x USB4 / Thunderbolt ports with DP alt mode and PD. Already tested the DP port with MST, running 2x 4K screens chained from that. And an OcuLink port

I have 2x 4K screens with USB-C/TB ports, and everything just works.. I'll probably be using the DP port with MST to hook up the screens, so i don't waste the bandwidth of the USB4/TB link for display, but still one USB-C will be connected to one screen, to use the USB ports in the screen, Even in that setup, KDE Wayland shows 3 available screens..

Took down the idle RPM's of the top fan alittle bit in BIOS, and now it's dead silent in idle.. Under load it's a non-annoying 'whoosh' sound..

Loaded mine with 96GB DDR5 5600, and 4TB SN850x

Now to install Fedora 41 with new KDE Plasma 5.3 on it..

 

[Wirko]

Great to hear that! Unfortunately the choice of SODIMMs is extremely limited if you want either something above 5600 MT/s or something above 2 x 32 GB.