Quick Answer

On X870E boards, M.2_1 is CPU-direct and runs at up to PCIe 4.0 x4 (7,000 MB/s) for Gen 4 NVMe or PCIe 5.0 x4 (14,000 MB/s) for Gen 5 NVMe if wired that way. M.2_2 and beyond are chipset-connected at PCIe 4.0 x4, sharing the chipset-to-CPU bandwidth with other devices. For SA gaming builds: install your OS and primary game drive in M.2_1 always. M.2_2 is fine for secondary game storage or overflow — the speed difference during gaming is under 0.5 seconds per load.

X870E M.2 Architecture Detail

X870E uses AMD's X670E (or refreshed X870E) dual-chipset silicon. The lane layout:

M.2_1 (CPU-direct):

  • Dedicated PCIe 4.0 x4 (7,000 MB/s Gen 4) or PCIe 5.0 x4 (14,000 MB/s Gen 5) depending on board
  • No shared bandwidth — dedicated CPU lanes
  • Lowest latency of all M.2 slots

M.2_2, M.2_3, M.2_4 (chipset-connected):

  • PCIe 4.0 x4 via chipset (X670E/X870E chipset to CPU: PCIe 4.0 x8 shared link)
  • Shared bandwidth with USB 3.2 Gen 2, SATA, other chipset devices
  • Under heavy concurrent I/O: 200–500 MB/s lower sustained throughput than M.2_1

Boards with two CPU-direct M.2 slots (premium X870E designs): ASUS ROG Crosshair X870E Hero includes M.2_1 (PCIe 5.0 x4) and M.2_2 (PCIe 4.0 x4), both CPU-direct — check your specific board's lane diagram.

Speed Benchmark Comparison

Scenario M.2_1 CPU-direct M.2_2 Chipset
Sequential read (idle system) 7,300 MB/s 7,000–7,200 MB/s
Sequential write (idle system) 6,600 MB/s 6,200–6,500 MB/s
Sequential read (USB 3.2 active) 7,300 MB/s 5,500–6,500 MB/s
Game load time (CS2 large map) 3.8s 4.1s

FAQ

If my X870E board has a PCIe 5.0 M.2 slot, is it always M.2_1?

Usually yes — PCIe 5.0 M.2 slots require CPU-direct lanes, which are always allocated to the primary M.2 slot. On premium X870E boards, M.2_1 may be PCIe 5.0 x4; lower slots are PCIe 4.0 chipset-connected. Confirm in your board's PCIe lane diagram (usually page 2–4 of the hardware manual).

Does secondary game storage in M.2_2 affect fps in CS2 on X870E?

No — game fps is determined by CPU and GPU, not storage speed once the game is loaded. M.2_2 chipset connectivity has no fps impact during gameplay. The 0.3-second slower load time on M.2_2 versus M.2_1 is the only measurable difference for gaming.

Can I install a Gen 5 NVMe in M.2_2 on an X870E board?

Yes — but it runs at Gen 4 speeds (7,000 MB/s) since M.2_2 is chipset-connected at PCIe 4.0 x4. Install Gen 5 drives only in the PCIe 5.0 M.2 slot (M.2_1 on supported boards) to get full 14,000+ MB/s performance.

TIP

X870E board's manual for a PCIe lane diagram before deciding which M.2 slot to use — some premium boards route M.2_2 through CPU-direct lanes as well (providing full PCIe 4.0 x4 speed without chipset sharing), which changes the slot priority recommendation entirely for dual-drive setups.