🧵 [SOLVED] Why doesn’t my ASUS B250 Mining Expert / ASRock H110 Pro BTC+ detect more than 8 GPUs? Real experience with 12× RTX 5070

Reflex007 · September 14, 2025, 2:43pm

If your B250 or H110 Pro BTC+ motherboard doesn’t detect the 9th to 12th GPU (especially under HiveOS + NVIDIA), the issue is not risers, power, or the cards themselves. It’s a system address space limitation (MMIO / BAR). Here’s the full journey and how we solved it.

Initial System Configuration:

Motherboard: ASUS B250 Mining Expert
CPU: Intel i3-9100F (also tested with G3900)
RAM: 16 GB DDR4
SSD: Patriot Burst 120 GB
PSUs: 2× Silverstone Hela 2500RZ (connected via ADD2PSU with relays)
Risers: PCIe x1 to x16, version 010 Plus
GPU: 12× Palit RTX 5070 GamingPro
OS: HiveOS (latest stable release)

The Problem:

System would consistently detect only 8 GPUs.
Adding a 9th GPU: fans spin, riser powers on, but GPU is not visible in nvidia-smi or HiveOS dashboard.
Swapping GPUs, risers, power rails did not change anything.
BIOS settings already included:

Above 4G Decoding → Enabled
CSM → Disabled
PCIe speed → Gen1 (for stability)

Step-by-step Troubleshooting

1. Tested all 12 GPUs individually:

Each card worked perfectly when connected solo or in smaller groups.

2. Tested all risers and power connections:

No faulty risers or cables.

3. Tried another board (H110 Pro BTC+):

Same issue — hard limit at 8 GPUs.

4. Analyzed system address usage with HiveOS:

Command used:

lspci -v -s <PCI address>

Example result per GPU:

Memory at f0000000 [size=64M]
Memory at 2010000000 [size=256M]
Memory at 2008000000 [size=32M]

So each RTX 5070 GPU takes up around 352 MB of MMIO memory space.

→ 12 × 352 MB ≈ 4.2 GB
→ Add chipset and BIOS overhead: requires ~6 GB MMIO space

Older chipsets like B250 or H110, especially with low-end CPUs (e.g. G3900), cannot allocate this much MMIO space even if “Above 4G Decoding” is enabled.

Solution: Hardware platform upgrade

New working setup:

Motherboard: TB560-BTC PRO
CPU: Intel i7-11700K
Same SSD, PSUs, risers, and GPUs
BIOS Settings:
- Above 4G Decoding → Enabled
- Re-BAR (Resizable BAR) → Disabled
- CSM → Disabled
- PCIe Speed → Gen1

Result: All 12× RTX 5070 GPUs now recognized and stable in HiveOS.

Key Takeaways

Configuration	Working GPU Count
B250 + G3900	6–8 GPUs max
B250 + i3-9100F	7–8 GPUs
H110 Pro BTC+ + G3900	6–8 GPUs
TB560 + G5900	9–11 GPUs (varies)
TB560 + i7-11700K	12 GPUs fully supported

Tips for building a 12-GPU rig:

Use modern motherboards (B560, Z590, etc.).
Choose at least a 10th or 11th Gen Intel CPU (e.g., i5‑10400, i7‑11700F/K).
BIOS setup:
- Enable Above 4G Decoding
- Disable Re-BAR (Resizable BAR) — not needed for mining
- Disable CSM (legacy boot)
- Set all PCIe lanes to Gen1 for maximum stability

If you’re experiencing similar problems…

I hope this post saves you hours of frustration. If you’re stuck, drop your specs and I’ll try to help.
Also, search Reddit for:

“B250 not detecting 9th GPU”

Maybe this thread will pop up and help others too.