PCIe Lanes && NVMe

[Derrk]

Not sure if this belongs in storage thread, mods can move it if they want (sorry)

 

Basically I'm considering getting a samsung 970. I'm using ryzen 2700x with an x470 f-gaming. I already have an m.2 but its only a sata drive. I'd be cloning my original m.2 onto the new nvme drive, putting the new one in my first m.2 slot, and putting the sata m.2 into the secondary slot.  

Now i have a pretty basic understanding of PCIe lanes, so i know my processor has 20 lanes, and the mobo has 2 pcie3 lanes, and 8 general purpose pcie2 lanes.

 

I know my gpu uses 16 lanes, and an NVMe uses 4 lanes, which would occupy all 20 lanes of my cpu. I also have a x1 pcie wireless card since my mobo doesn't have one built-in. I figure this lane would be used by the motherboard rather than the cpu.

I guess what i'm uncertain about is which lanes belong to the motherboard, which lanes belong to the cpu, and what (if any) are shared?

 

will adding an NVMe to my build compromise any of the PCIe lanes from my graphics card? Is my system still optimized for NVMe?

 

 

I hope this wasn't too confusing. I can try to clarify anything if it was. Any help is appreciated.

[Zagna]

Ryzen has 24 PCIe 3.0 lanes

• 16x for graphics, which on X370/X470 platforms can split to 8x/8x
• 4x for dedicated NVMe
• 4x for chipset connection
  • Chipset has 8 PCIe 2.0 lanes

Your GPU will use the 16x, NVMe the 4x, old M.2 will use one of the chipsets SATA ports and wireless card also uses the chipsets PCIe 2.0 port.

[Derrk]

1 minute ago, Zagna said:

Ryzen has 24 PCIe 3.0 lanes

• 16x for graphics, which on X370/X470 platforms can split to 8x/8x
• 4x for dedicated NVMe
• 4x for chipset connection
  • Chipset has 8 PCIe 2.0 lanes

Your GPU will use the 16x, NVMe the 4x, old M.2 will use one of the chipsets SATA ports and wireless card also uses the chipsets PCIe 2.0 port.

thank you for clearing that up for me. I think i read somewhere that if both m.2 slots are occupied, it'll reduce the number of SATA ports i can use from 6 to 4. Does this sound right?

[Zagna]

5 minutes ago, Derrk said:

thank you for clearing that up for me. I think i read somewhere that if both m.2 slots are occupied, it'll reduce the number of SATA ports i can use from 6 to 4. Does this sound right?

The 4x NVMe block can be configured as 4x PCIe 3.0, 2x PCIe 3.0 & 2x SATA or 2x SATA. Most boards support either 4x PCIe 3.0 or 2x SATA only.

So there are 2 "A(PU) SATA" ports on a number of AM4 boards. If a SATA M.2 is put into the primary M.2, one of the ASATA ports is disabled but other works. With a NVMe drive, both ASATA ports are disabled.

Some boards don't have any ASATA ports and rather use the chipsets SATA ports only and maybe also an additional Asmedia SATA controller for more ports.

And the second M.2 usually uses 4x PCIe 2.0 lanes from the chipset and a single SATA port from the chipset.

So if both M.2 have a SATA SSD, you're using up 1 ASATA port and 1 chipset SATA port.

[Sakkura]

7 minutes ago, Derrk said:

thank you for clearing that up for me. I think i read somewhere that if both m.2 slots are occupied, it'll reduce the number of SATA ports i can use from 6 to 4. Does this sound right?

Depends how the motherboard is configured, but not necessarily. The chipset actually supports up to 8 SATA ports, so even with 2 shared with an M.2 slot the board can still have 6 regular SATA ports independently. That is the case with your board.

 

The second M.2 slot does, however, share a PCIe clock with some of the PCIe slots which will be disabled if you install a PCIe drive in that M.2 slot. But that's not an issue with a SATA M.2 drive.

[Derrk]

7 minutes ago, Zagna said:

The 4x NVMe block can be configured as 4x PCIe 3.0, 2x PCIe 3.0 & 2x SATA or 2x SATA. Most boards support either 4x PCIe 3.0 or 2x SATA only.

So there are 2 "A(PU) SATA" ports on a number of AM4 boards. If a SATA M.2 is put into the primary M.2, one of the ASATA ports is disabled but other works. With a NVMe drive, both ASATA ports are disabled.

Some boards don't have any ASATA ports and rather use the chipsets SATA ports only and maybe also an additional Asmedia SATA controller for more ports.

And the second M.2 usually uses 4x PCIe 2.0 lanes from the chipset and a single SATA port from the chipset.

So if both M.2 have a SATA SSD, you're using up 1 ASATA port and 1 chipset SATA port.

 

2 minutes ago, Sakkura said:

Depends how the motherboard is configured, but not necessarily. The chipset actually supports up to 8 SATA ports, so even with 2 shared with an M.2 slot the board can still have 6 regular SATA ports independently. That is the case with your board.

 

The second M.2 slot does, however, share a PCIe clock with some of the PCIe slots which will be disabled if you install a PCIe drive in that M.2 slot. But that's not an issue with a SATA M.2 drive.

Thank you everyone. You made this painless after some very painful/unsuccessful research