ASUS PRIME B850M-K AM5 mATX Motherboard - DDR5, PCIe 5.0
ASUS
ASUS PRIME B850M-K AM5 mATX Motherboard - DDR5, PCIe 5.0
The ASUS PRIME B850M-K is a micro-ATX motherboard built around the AMD AM5 platform for PC builders who want a solid foundation for AMD Ryzen 9000, 8000, and 7000 series processors without overengineering the budget. It pairs an 8+2+1 phase digital power design with PCIe 5.0 storage and graphics support, 2.5Gb Ethernet, and Aura Sync RGB headers in a compact form factor suited to smaller builds.
Why this product
PCIe 5.0 for graphics and fast storage
One PCIe 5.0 x16 slot handles a discrete GPU, while the primary M.2 slot supports PCIe 5.0 x4 for storage speeds up to 128 Gbps — keeping the platform ready for the fastest drives available.
8+2+1 phase digital power design
Discrete MOSFETs and a six-layer PCB help distribute heat around the voltage regulators, giving the CPU stable power delivery and headroom for overclocking.
DDR5 with EXPO and AEMP support
Two DIMM slots accept up to 128 GB of DDR5, with support for AMD EXPO and ASUS AEMP profiles to push memory speeds well beyond JEDEC defaults.
BIOS FlashBack for easy firmware updates
The rear-panel BIOS FlashBack button lets you update firmware from a USB drive without a CPU or memory installed — useful before fitting a new processor.
2.5Gb Ethernet with LANGuard protection
A Realtek 2.5Gb port delivers faster wired transfers than standard Gigabit connections, and ASUS LANGuard adds overvoltage and ESD protection to the port.
Three Addressable RGB Gen 2 headers
Three ARGB Gen 2 headers auto-detect LED counts on connected devices and synchronise lighting through Aura Sync and Armoury Crate software.
- SocketAMD AM5
- ChipsetAMD B850
- Form FactorMicro-ATX (9.6 in × 8.7 in / 24.4 cm × 22.1 cm)
- Memory2 x DDR5 DIMM, max. 128 GB
- Primary M.2 SpeedPCIe 5.0 x4 (up to 128 Gbps)
- Ethernet2.5Gb (Realtek)
- Rear USB2× USB 10Gbps Type-A, 2× USB 5Gbps Type-A, 4× USB 2.0 Type-A
- ARGB Headers3 × Addressable RGB Gen 2
- SKUASU-2691
- EAN4711636005517
- Fits AMD Socket AM5 — compatible with AMD Ryzen 9000, 8000 and 7000 series desktop processors.
- Supports DDR5 memory modules (non-ECC and ECC unbuffered) in a dual-channel configuration.
- Micro-ATX form factor (9.6 in × 8.7 in / 24.4 cm × 22.1 cm) — fits standard mATX and full-ATX cases.
- The primary PCIe x16 slot runs at x16 mode with Ryzen 9000/7000 processors, but drops to x8/x4 mode with Ryzen 8000 series processors.
- RAID 5 and RAID 10 support depends on the processor: Ryzen 9000 supports RAID 0/1/5/10; Ryzen 8000 supports RAID 0/1 only; Ryzen 7000 supports RAID 0/1/10.
- Does not support AMD AM4 processors — this board is AM5 only and is not backward-compatible with older Ryzen generations.
Best for
- First-time and DIY builders who want BIOS FlashBack, EZ DIY BIOS features, and bundled SATA cables to reduce the friction of a first build.
- Compact desktop builds where a micro-ATX footprint is needed but PCIe 5.0 storage and a discrete GPU slot are still required.
- Ryzen 9000 series owners who want a B850 platform with full PCIe 5.0 x16 graphics support and PCIe 5.0 M.2 storage.
- RGB-focused builds on a budget — three Addressable RGB Gen 2 headers cover a well-decorated system without needing a separate controller.
- Wired-network users who benefit from a 2.5Gb Ethernet port rather than standard Gigabit, without paying for a discrete NIC.
Trade-offs
- Multi-GPU or high-lane-count workstation builds — only two PCIe slots are present, one at x16 (CPU) and one at x4 (chipset), leaving no room for additional expansion cards.
- Builders who need more than two M.2 drives onboard — the board provides exactly two M.2 slots, so additional NVMe storage requires SATA ports or an add-in card.
- Wireless-only households — there is no onboard Wi-Fi or Bluetooth; a separate adapter is required for wireless connectivity.
- Builds needing more than two memory slots — with only two DIMM slots, future memory upgrades are limited to replacing existing modules rather than adding new ones.
- Ryzen 8000 series users needing full PCIe 5.0 GPU bandwidth — the primary slot is limited to PCIe 4.0 x8/x4 mode with that processor family.
ASUS Prime series motherboards are expertly engineered to unleash the full potential of AMD Ryzen™ 9000 series processors. The PRIME B850M-K 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.
Digital Power Design
PRIME B850M-K 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.
Enhanced DDR5 Performance
Comprehensive memory tuning options are the cornerstone of PRIME motherboards. The PRIME B850M-K maximizes the potential of your DDR5 modules, from entry-level to extreme-speed kits.
Two M.2 slots (up to 128 Gbps)
PRIME B850M-K offers a total of two M.2 slots, including one that supports data-transfer speeds of up to 128 Gbps via PCIe 5.0, and one that supports PCIe 4.0. This enables quicker boot-up and app load times with OS or application drives.
Cooler by Design
PRIME B850M-K 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. ASUS Fan Xpert 2+ software provides comprehensive control over fans. An Auto-Tuning mode intelligently configures all parameters with a single click. Each onboard header supports auto-detection of PWM or DC fans. Each header can dynamically reference three thermal sensors.
Aura Sync
Three Addressable RGB Gen 2 headers detect LED counts on compatible RGB devices, automatically adjusting lighting effects accordingly. Customize Aura Sync RGB and control ASUS devices with Armoury Crate. Complete RGB lighting control for enthusiast systems, ensuring seamless synchronization with compatible hardware.
General
| Brand | ASUS |
|---|---|
| Form Factor | Micro-ATX |
| Dimensions | 9.6 in × 8.7 in (24.4 cm × 22.1 cm) |
| CPU Socket | AMD AM5 |
| Chipset | AMD B850 |
| Supported Processors | AMD Ryzen 9000, 8000 & 7000 Series Desktop (up to 170W) |
| Operating System | Windows 11, Windows 10 64-bit |
| BIOS | 256 Mb Flash ROM, UEFI AMI BIOS |
Memory & Storage
| Memory Slots | 2 x DIMM (DDR5) |
|---|---|
| Max Memory | 128 GB |
| Memory Speed (OC) | Up to 8200+ MT/s (Ryzen 9000), 9600+ MT/s (Ryzen 8000), 8000+ MT/s (Ryzen 7000) |
| Memory Profiles | AMD EXPO, ASUS AEMP |
| M.2 Slots | 2 × (Key M) |
| M.2_1 | Type 2280, PCIe 5.0 x4 (up to 128 Gbps) |
| M.2_2 | Type 2242/2260/2280, PCIe 4.0 x4 |
| SATA Ports | 4 × SATA 6Gb/s |
| RAID Support | RAID 0/1/5/10 (Ryzen 9000); RAID 0/1 (Ryzen 8000); RAID 0/1/10 (Ryzen 7000) |
Connectivity & Expansion
| PCIe Slots | 1 × PCIe 5.0 x16 (CPU, Ryzen 9000/7000); 1 × PCIe 4.0 x16 (chipset, x4 mode) |
|---|---|
| Ethernet | 1 × Realtek 2.5Gb with ASUS LANGuard |
| Rear USB | 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 × USB 2.0 headers |
| Video Output | 1 × HDMI 2.1 (4K@60Hz), 1 × DisplayPort 1.4 (8K@30Hz) |
| Audio | 3 × rear audio jacks, 1 × front panel audio header, 1 × S/PDIF out header |
| Legacy I/O | 1 × PS/2 Keyboard/Mouse combo port |
Power, Cooling & Headers
| Power Design | 8+2+1 phase digital VRM with discrete MOSFETs |
|---|---|
| PCB Layers | Six-layer |
| Power Connectors | 1 × 24-pin ATX, 1 × 8-pin +12V CPU |
| Fan Headers | 1 × 4-pin CPU fan, 3 × 4-pin chassis fan |
| ARGB Headers | 3 × Addressable RGB Gen 2 |
| BIOS FlashBack | Yes (rear-panel button) |
| Other Headers | Clear CMOS, COM port, SPI TPM (14-1 pin), system panel |
| Accessories Included | 2 × SATA 6Gb/s cables, I/O shield, M.2 rubber package, M.2 screw package, quick start guide |
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.