ASUS PRIME B850M-A-CSM mATX Motherboard - AMD B850, AM5
ASUS
ASUS PRIME B850M-A-CSM mATX Motherboard - AMD B850, AM5
The ASUS PRIME B850M-A-CSM is a compact mATX motherboard for AMD Ryzen 9000, 8000 and 7000 series processors. It combines an 8+2+1 phase power design with PCIe 5.0 connectivity and three M.2 slots to handle modern gaming, content creation and AI workloads in a smaller form factor.
Why this product
PCIe 5.0 storage and graphics slots
The M.2_1 slot supports PCIe 5.0 x4 drives at up to 128 Gbps, and the primary expansion slot handles PCIe 5.0 graphics cards on Ryzen 9000 series. Older Ryzen 7000 and 8000 series use PCIe 4.0 for GPU and M.2.
8+2+1 phase power delivery with Digi+ VRM
Discrete MOSFETs and real-time voltage control provide stable, efficient power to the CPU and memory, with headroom for overclocking.
DDR5 overclocking with EXPO and AEMP support
ASUS Enhanced Memory Profile and AMD EXPO give you easy one-click profiles and extensive manual tuning options for high-speed memory kits.
Compact mATX size with full connectivity
At 9.6 × 9.6 inches, it fits smaller cases while retaining 2.5Gb Ethernet, multiple USB ports, three M.2 slots and four SATA drives.
Dual display output and AI-ready firmware
Two DisplayPort outputs and one HDMI port support up to 8K on DP and 4K on HDMI. The board is optimized for Advanced AI PC applications.
- SocketAMD AM5
- ChipsetAMD B850
- Form FactormATX (9.6 × 9.6 inch)
- Memory Slots4 × DIMM DDR5 (max. 256GB)
- M.2 Slots3 (PCIe 5.0 x4, PCIe 4.0 x4, PCIe 4.0 x4)
- SATA Ports4
- GPU Slot1 × PCIe slot (mode varies by CPU gen)
- Rear USB2× USB 10Gbps Type-A, 2× USB 5Gbps Type-A, 4× USB 2.0
- SKUASU-2711
- EAN4711636054720
- Fits AMD Socket AM5 processors: Ryzen 9000, 8000 and 7000 series, up to 170W TDP.
- Supports DDR5 memory at stock and overclocked speeds up to 8000+ MT/s via EXPO and AEMP.
- Accepts NVMe M.2 drives in all three slots: PCIe 5.0 on M.2_1 and PCIe 4.0 on M.2_2 and M.2_3.
- Ships with Windows 11 and Windows 10 64-bit support; includes BIOS FlashBack for easy firmware updates.
- PCIe 5.0 GPU slot operates at x16 on Ryzen 9000, but drops to x8/x4 on Ryzen 8000 and x1 on Ryzen 7000.
Best for
- Ryzen 9000 owners seeking full PCIe 5.0 support on GPU and NVMe storage
- Small-form-factor builders who need mATX dimensions without sacrificing three M.2 slots and modern connectivity
- DDR5 overclockers and memory enthusiasts, thanks to EXPO, AEMP and extensive UEFI tuning
- AI and content-creation workloads on a budget, with AI PC-ready firmware and 2.5Gb Ethernet
- Users who want real-time voltage control and overclocking headroom via the Digi+ VRM module
Trade-offs
- Ryzen 7000 owners: the GPU slot operates at PCIe 4.0 x1 instead of x16, severely limiting graphics performance
- Ryzen 8000 users: PCIe 5.0 features are unavailable; GPU slot runs PCIe 4.0 x8/x4 only
- Builders needing many SATA drives or extensive expansion; only four SATA ports and three total M.2 slots are available
- Systems requiring advanced RAID: Ryzen 8000 supports only RAID 0/1, and Ryzen 7000 excludes RAID 5
ASUS Prime series motherboards are expertly engineered to unleash the full potential of AMD Ryzen™ 9000 series processors. The PRIME B850M-A-CSM motherboard provides users and PC DIY builders with a range of performance optimizations via intuitive software and firmware features. It's designed to be Advanced AI PC-ready, offering the power and connectivity needed for demanding AI applications.
PRIME B850M-A-CSM features an 8+2+1 phase power design with discrete MOSFETs, ensuring efficient and stable power delivery for AMD processors plus steady performance for day-to-day use. The multi-layered printed circuit board design quickly dissipates heat around the voltage regulators to improve overall system stability and provide the CPU with more overclocking headroom. The Digi+ voltage-regulator module (VRM) delivers real-time control over voltage droop, automatically switching frequency and power-efficiency settings.
Comprehensive memory tuning options are the cornerstone of PRIME motherboards. The PRIME B850M-A-CSM maximizes the potential of your DDR5 modules, from entry-level to extreme-speed kits. For those looking to surpass stock DDR5 speeds, the PRIME B850M-A-CSM offers extensive AMD Extended Profiles for Overclocking (EXPO™) support and a wide array of UEFI settings for further performance tweaks.
PRIME B850M-A-CSM offers a total of three M.2 slots, including one that supports PCIe 5.0 x4 mode (up to 128 Gbps). The PRIME B850M-A-CSM motherboard is engineered with multiple onboard heatsinks and an array of hybrid fan headers to help ensure your rig stays cool and stable under intense workloads.
General
| Brand | ASUS |
|---|---|
| Product Line | PRIME Series |
| Socket | AMD AM5 |
| Supported Processors | AMD Ryzen 9000, 8000, 7000 series (up to 170W TDP) |
Memory & Storage
| Memory Slots | 4 × DIMM DDR5 |
|---|---|
| Max Memory | 256GB |
| Memory Speed Support | Up to 8000+ MT/s (OC) with Ryzen 9000/8000/7000 |
| Memory Features | EXPO, AEMP, ECC/Non-ECC support |
| M.2 Slot 1 | 2280, PCIe 5.0 x4 (up to 128 Gbps) |
| M.2 Slot 2 | 2280, PCIe 4.0 x4 |
| M.2 Slot 3 | 2242/2260/2280, PCIe 4.0 x4 |
| SATA Ports | 4 × 6Gb/s |
| RAID Support | Varies by CPU series (Ryzen 9000: 0/1/5/10; 8000: 0/1; 7000: 0/1/10) |
Power & Cooling
| Power Phases | 8+2+1 with discrete MOSFETs |
|---|---|
| VRM Type | Digi+ with real-time voltage control |
| Power Connectors | 24-pin ATX, 8-pin +12V CPU, 4-pin +12V CPU |
| CPU Fan Headers | 1 × 4-pin CPU, 1 × 4-pin CPU OPT, 1 × 4-pin AIO Pump |
| Chassis Fan Headers | 3 × 4-pin |
| Fan Control | ASUS FAN Xpert 2+ |
| PCB Layers | 6-layer with multi-stage heat dissipation |
Connectivity & I/O
| Ethernet | 1 × Realtek 2.5Gb with LANGuard |
|---|---|
| GPU Expansion Slot | 1 × SafeSlot (PCIe 5.0 x16 on Ryzen 9000; PCIe 4.0 x8/x4 on Ryzen 8000; PCIe 4.0 x1 on Ryzen 7000) |
| Secondary Expansion | 1 × PCIe 4.0 x16 slot (x1 mode) |
| Rear USB Ports | 2 × USB 10Gbps Type-A, 2 × USB 5Gbps Type-A, 4 × USB 2.0 Type-A |
| Front USB Headers | 1 × USB 5Gbps Type-C connector, 1 × USB 5Gbps header (2 ports), 2 × USB 2.0 headers (4 ports) |
| Audio Output | 1 × S/PDIF header, 1 × Front Panel Audio header |
| Video Output | 2 × DisplayPort (max. 8K@30Hz), 1 × HDMI (max. 4K@60Hz) |
| RGB Headers | 3 × Addressable RGB Gen 2 |
BIOS & Features
| BIOS Flash ROM | 256 Mb |
|---|---|
| BIOS Type | UEFI AMI |
| BIOS Features | BIOS FlashBack, Q-LED Core diagnostics |
| AI PC Support | Advanced AI PC-ready |
| RGB Lighting Control | ASUS Aura Sync |
| I/O Shield | Pre-mounted |
Physical Specifications
| Form Factor | mATX |
|---|---|
| Board Dimensions | 9.6 × 9.6 inch (24.4 × 24.4 cm) |
System Requirements
| Operating System | Windows 11, Windows 10 64-bit |
|---|
Shipping
All our products are shipped from the United Kingdom within 24 to 48 hours of purchase. See our Shipping and Returns page for full details.
Returns
- Tech Syndicate offers a full money-back guarantee on all purchases made in our store. If you are not satisfied with your purchase, we will provide a full refund, no questions asked.
- Refunds are available within 45 days of delivery.
- After the 45-day period you are no longer eligible for a refund, so we encourage you to try the product within the first few weeks to make sure it fits your needs.