Question My motherboard and it'sM.2 slots

knght990

Member
Jun 3, 2006
178
9
81
I bought a Asus TUF x570 and I can't figure out the m.2 slots.

I can't find in the manual or on the website, how the m.2s are controlled. Are they both CPU, or one CPU and the other chipset?
I would assume the slot near the CPU is CPU controlled and the one near the chipset is chipset controlled.
The board comes with one heat spreader and a foam support square pre-installed on the lower m.2 slot. They don't appear to be movable to the upper slot. As much as I probably don't need a heat spreader on my drive, I doubt it could do harm.

So, I'm trying to figure out:
1. What controls each m.2 slot on this board
2. How did you find the answer so I can do it in the future
3. Why Asus seems to assume the lower slot is the preferable one by installing the heat spreader there.

Any help is appreciated.
 

Iron Woode

Elite Member
Super Moderator
Oct 10, 1999
30,994
12,541
136
I have the Asus X570-P which is nearly identical to yours.

All the reading I have done implies the top slot is cpu controled while the lower one isn't.
 
  • Like
Reactions: knght990

knght990

Member
Jun 3, 2006
178
9
81
I have the Asus X570-P which is nearly identical to yours.

All the reading I have done implies the top slot is cpu controled while the lower one isn't.
Would you have a guess as the why Asus put the heat spreader on the lower slot, I would have assumed the CPU slot to be primary (previous thread I posted)
 

Iron Woode

Elite Member
Super Moderator
Oct 10, 1999
30,994
12,541
136
Would you have a guess as the why Asus put the heat spreader on the lower slot, I would have assumed the CPU slot to be primary (previous thread I posted)
could be that they prefer you to use the lower slot. On my board that slot has room for longer drives.
 

knght990

Member
Jun 3, 2006
178
9
81
I sent ASUS an email earlier today but I don't expect to hear back until the new year.

I installed my m.2 to the lower slot on two assumptions,
1. ASUS "recommendation" due to their heat spreader installation
2. I need a heat spreader for the m.2

But I suspect from another conversation I had that installing it to the top slot would be better as it is probably run by the CPU which might make it slightly more efficient.

Does that make sense or does it pretty much not matter?

I got one of those Sabrent heat-pipe spreaders for the other slot, which is probably totally unnecessary. I just like the way it looks and because I could.
 

damian101

Senior member
Aug 11, 2020
291
107
86
But I suspect from another conversation I had that installing it to the top slot would be better as it is probably run by the CPU which might make it slightly more efficient.

Does that make sense or does it pretty much not matter?
The chipset is connected with 4 PCIe 4.0 lanes to the CPU, so all the chipset PCIe lanes have to share that bandwidth. Don't know about any effects on access times.
 

knght990

Member
Jun 3, 2006
178
9
81
The chipset is connected with 4 PCIe 4.0 lanes to the CPU, so all the chipset PCIe lanes have to share that bandwidth. Don't know about any effects on access times.

I saw that. I'm considering rather than sharing the chipset's 4 lanes among 4 sata SSDs, 1 pcie 3.0 drive, and the regular USB ports, it would be better to have the pcie 3.0 m.2 on the cpu's dedicated 4 lanes. (per x570 block diagram) But the motherboard manual and documentation doesn't clearly indicate to me how the m.2s were assigned.
 

knght990

Member
Jun 3, 2006
178
9
81
ASUS replied to my email, but were a bit vague. They replied M.2 slot 1 is the intended primary slot. In my case, the one that didn't come with the heatsink.

I will ask for more direct clarification of PCIe lane assignments.

I did buy an extra m.2 heat sink, the sabrent one, mostly because I could.
 
Last edited:
  • Like
Reactions: Iron Woode

Hail The Brain Slug

Diamond Member
Oct 10, 2005
3,490
2,418
136
Top slot is CPU lanes, bottom is chipset.

I've just learned this is an important distinction myself as I bought two brand new high end PCI-e 4.0 drives expecting to install them into both m.2 slots on my asus x570 board.

Turns out the bottom m.2 driven by chipset lanes is slower, likely because the chipset only connects to the CPU via 4 lanes and it has to share that bandwidth with all of the I/O the chipset provides.

My WD SN850 2TB:
unknown-31.png

My Sabrent Rocket 4 Plus 2TB
unknown-19.png

Now oddly enough, the Rocket 4 Plus took a significantly worse hit being in the M.2_2 slot than the SN850. This was on the 12/7 UEFI 3003 version which looks to also be the latest version for your board. (Yours is numbered differently but it's dated 12/8 and has the same patch notes)

Dark Hero got a beta bios with AGESA 1.1.9.0 posted yesterday and I updated immediately after running this test and ran it again.

Surprisingly, it corrected almost all of this performance deficit from M.2_2. It still is a bit of a bottlebeck for straight sequential and limiting it to ~6500MB/s on either drive in crystaldiskmark from their potential of 7000+ in M.2_1, but in Anvil it is clear the overall performance was corrected and is within 2000 points of the top slot (vs the awful drop of 7500 points previously).

I doubt the slot selection makes a difference if you are running PCI-e 3.0 drives, after the UEFI bug was corrected in my case it appears the limit is just a raw bandwidth limit. Can't hit it unless your drive is capable of >6000MB/s.
 
Last edited:
  • Like
Reactions: knght990

knght990

Member
Jun 3, 2006
178
9
81
I assumed when I bought the motherboard that these things would be true because of the x570 block diagram. It just wasn't confirmed by the manual and it got me thinking they may not have to follow intended architecture. I don't know much about how boards are designed so this is partly learning more for me.
In my current configuration, I should be 2 lanes for my m.2_2 and 2 for the SATA drives.
I've only benched the drives in CPUZ. It indicates I make max speed on my PCIe 3.0 m.2 in slot m.2_2, but I don't know where it measures the speeds.
Is there a free or inexpensive version of a drive speed bench that tests through to the CPU?
 
Last edited:

Hail The Brain Slug

Diamond Member
Oct 10, 2005
3,490
2,418
136
I assumed when I bought the motherboard that these things would be true because of the x570 block diagram. It just wasn't confirmed by the manual and it got me thinking they may not have to follow intended architecture. I don't know much about how boards are designed so this is partly learning more for me.
In my current configuration, I should be 2 lanes for my m.2_2 and 2 for the SATA drives.
I've only benched the drives in CPUZ. It indicates I make max speed on my PCIe 3.0 m.2 in slot m.2_2, but I don't know where it measures the speeds.
Is there a free or inexpensive version of a drive speed bench that tests through to the CPU?

CrystalDiskMark should do the trick.

However the chipset should be offering up 4 lanes to that M.2 slot, as the chipset has 8 lanes to share in addition to all of the I/O it provides for USB, SATA, etc.

I am unsure if it multiplexes its lanes or if it offers 8 lanes itself then turns around and routes the data through its own 4 lanes to the CPU.

The problem this provides is you have 8 4.0 lanes and all the I/O offered by the chipset limited to maximum simultaneous bandwidth of 4x 4.0 lanes (its connection to the CPU). This is the issue I believe I am observing connecting a PCI-e 4.0 drive that is capable of fully saturating all 4 lanes.

I believe a 3.0 drive should connect with 4 lanes and have no throughput cap.