Please help me understand these Mobo specs

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Guarateed_12

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I was looking at the specs for the new Asus Apex board. It says that with a Ryzen 9000 series CPU the following specs apply...

There are 3 M.2 slots (M.2_1, M.2_2, M.2_3) and all are PCIe 5.0 x4 mode. But further down the spec sheet it states... "When M.2_3 are enabled, PCIEX16_1 will run x8 and PCIEX16_2 will run x4, M.2_2 will be disabled"

I understand the throttling of the PCIEX16 slots but I'm having a problem understanding the "Disabled" statement. Are they saying if I run an M.2 drive in slot 2_3 that slot 2_2 is effectively dead? Are they basically saying if you want all 3 M.2 slots to work that you can't populate the PCIE slots? Sorry if this is a N00b question but I'm not up to speed on newer mobo specs etc.
 
* Please check the PCIe bifurcation table on the support site (https://www.asus.com/support/FAQ/1037507/).
**When both PCIEX16_1 and PCIEX16_2 are in use, they will each run in x8 mode.
***When M.2_2 is enabled, but M.2_3 is not in use, PCIEX16_1 will run in x8 mode and PCIEX16_2 will be disabled.
***When M.2_3 is enabled, but M.2_2 is not in use, PCIEX16_1 will run in x8 mode and PCIEX16_2 will run in x4 mode.
***When both M.2_2 and M.2_3 are enabled, PCIEX16_1 will run in x8 mode and PCIEX16_2 will be disabled.
- To ensure compatibility of the device installed, please refer to https://www.asus.com/support/ for the list of supported

You can use both m.2 slots, but you will lose a pcie slot (PCIEX16_2). You can use a single m.2 slot (M.2_3), and two PCIe slots, but one will be only 4 lanes (PCIEX16_2). If you use M.2_2, one PCIe slot will be disabled (PCIEX16_2).
 
That's assuming you were talking about the X870 Apex board.
 
There are only so many PCIe lanes on consumer boards. You either get m.2 slots or motherboard PCIe slots (greatly simplified explanation). You have to follow the description that Nobu posted to see the breakdown of what you can use together.
 
Assuming it's an Asus ROG Crosshair X870e APEX you're looking at...

They're fanning out the 16 PCI-e 5.0 lanes for the vid card all over the place.

You always get:
1 PCI-e 5.0 M.2 off the CPU
2 PCI-e 4.0 M.2 off the chipset - these are "DIMM.2" slots, but that just means you have to use an adapter to plug an M.2 in. It's a space saving thing. M.2s will probably stick up rather than be flush with the board under a heatsink.
1 PCI-e 4.0 4x slot off the chipset
1 PCI-e 3.0 1x slot off the chipset

Then you have the choice of these PCI-e 5.0 device combinations (plus the one always on M.2 above):
1 16x slot
2 8x slots
1 8x slot, 1 4x slot and 1 M.2
1 8x slot and 2 M.2

I don't see anything about USB4 sharing anything. On some boards using the USB4 turns something else off.
 
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First of all thank you to everyone who has responded.

Please excuse the lack of depth in my understanding. I do understand the concept of the different lanes that are available and to some extent how they work and the tradeoffs they present i.e. chipset vs CPU. But I don't understand this enough to describe it as technically as you might require so please bare with me.

As in my original post let's use the new Asus Apex 870E board and I'm using a Ryzen 9000 series CPU. My goal (or expectations) are to Install a non-gaming entry level GPU. If all 16 lanes aren't used I see no problem with it running at x8. Next I have a an RME Audio "audio interface" that is PCIe x 1. I would then like to populate all 3 onboard M.2 slots. Would this configuration allow me to take advantage of all the M.2 slot's capabilities?
 
If you're not technical why are you looking into getting the memory overclocking model over a regular variant? Have extra money to burn?
 
D-EJ915 said:
If you're not technical why are you looking into getting the memory overclocking model over a regular variant? Have extra money to burn?
Click to expand...

I don't have any plans on buying that Mobo. I thought this might be a relatable configuration and I could use it in order to help me understand what I've asked in my previous questions and examples.
 
Guarateed_12 said:
I don't have any plans on buying that Mobo. I thought this might be a relatable configuration and I could use it in order to help me understand what I've asked in my previous questions and examples.
Click to expand...
Ok, I was going to advise against buying it as for 99% of people it won't increase any performance over a normal model.
 
I just want to understand how all this works together. If I buy a board with 3 M.2 slots I want to make sure once I populate at least 2 of the PCIe slots that the M.2's will run as expected.
 
Guarateed_12 said:
I just want to understand how all this works together. If I buy a board with 3 M.2 slots I want to make sure once I populate at least 2 of the PCIe slots that the M.2's will run as expected.
Click to expand...
Generally speaking if a board has M.2 slots you can use them. It just might turn something else off. The thing you need to watch out for if you need 2 slots and 3 M.2 is one of the M.2s sharing lanes with a 4x slot off the chipset.

For a non-gaming build with an entry level vid card a board that has multiple PCI-e 5 M.2 slots can be good. On the other hand it's easy and usually quite a bit less expensive to get one PCI-e 5 off the CPU and two PCI-e 4 M.2s off the chipset. A lot of boards can use 3 M.2s, a full 16X vid card slot, and a 4x slot off the chipset. That's probably the least costly option. If you need two faster slots on a desktop board, some can do an 8x/8x split on the vid card slot lanes.
 
Guarateed_12 said:
Thank you.
Click to expand...
It really depends on what board you are looking at to get the real picture of whether it'll work for you or not since they're all so different so if you have questions about other ones post it here and we can take a look.
 
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