ASUS PRIME B840M-K, AMD B840, Socket AM5, micro ATX
Overview
ASUS Prime series motherboards are expertly engineered to unleash the full potential of AMD Ryzen™ 9000 series processors. The PRIME B840M-K provides users and PC DIY builders with a range of performance optimisations via intuitive software and firmware features. It is designed to be Advanced AI PC-ready, offering the power and connectivity needed for demanding AI applications.
Memory & Storage
DDR5 Support
The PRIME B840M-K supports DDR5-SDRAM across 2 DIMM slots in dual-channel configuration, with ECC & Non-ECC unbuffered memory support and a maximum capacity of 128 GB.
M.2 & SATA Storage
Two M.2 (M-key) slots for NVMe SSDs, plus 4× SATA III connectors supporting up to 6 storage drives in total. RAID 0, 1, 5, and 10 are supported across HDD and SSD configurations.
Connectivity
Rear I/O Summary: 2× USB 2.0 Type-A, 4× USB 3.2 Gen 1 Type-A, 1× HDMI, 1× RJ-45 (2.5GbE). No Wi-Fi onboard.
2.5 Gigabit Ethernet
Realtek 2.5GbE wired networking for fast, reliable connectivity.
Front Panel USB
Internal headers include 2× USB 2.0 and 2× USB 3.2 Gen 1 connectors for front-panel ports.
Expansion Slots
1× PCIe 4.0 x16 (primary GPU slot), 1× PCIe 3.0 x16, and 2× M.2 (M-key) slots for NVMe storage.
Audio
7.1-channel onboard audio with front panel audio header and S/PDIF out connector.
Design & Aesthetics
Black PCB, micro ATX form factor (244 × 221 mm). Three addressable Gen 2 RGB headers (ARGB) for Aura Sync lighting synchronisation. Customise via Armoury Crate software.
DIY-Friendly Features
BIOS FlashBack™ — update BIOS without a CPU or RAM installed via USB.
Pre-Mounted I/O Shield — factory-installed for a cleaner, faster build.
Q-LED Core — colour-coded POST diagnostic LEDs for quick troubleshooting.
Software
UEFI BIOS (AMI) — 256 Mbit, supports Windows 10 x64 and Windows 11.
ASUS DriverHub — automatic driver detection and one-click installation.
Armoury Crate — RGB control, device management, product registration and updates.
What's Included
ASUS PRIME B840M-K motherboard, SATA cables, screws, pre-mounted I/O shield, documentation.
Technical Specifications
Processor
| Processor Manufacturer | AMD |
| Processor Socket | Socket AM5 |
| Compatible Processor Series | AMD Ryzen 7000 Series, AMD Ryzen 8000 Series, AMD Ryzen 9000 Series |
| Supported Processor Sockets | Socket AM5 |
Chipset & Form Factor
| Motherboard Chipset | AMD B840 |
| Chipset Family | AMD |
| Form Factor | micro ATX |
| Product Colour | Black |
| OS Support | Windows 10 x64, Windows 11 |
Memory
| Supported Memory Types | DDR5-SDRAM |
| Memory Slots | 2× DIMM |
| Memory Channels | Dual-channel |
| Maximum Memory | 128 GB |
| ECC Compatibility | ECC & Non-ECC |
| Unbuffered Memory | Yes |
Storage Controllers
| Supported Drive Types | HDD & SSD |
| Storage Interfaces | M.2, SATA III |
| Total Storage Drives Supported | 6 |
| HDDs Supported | 4 |
| RAID Support | Yes — 0, 1, 5, 10 |
Expansion Slots
| PCIe 4.0 x16 Slots | 1 |
| PCIe 3.0 x16 Slots | 1 |
| M.2 (M) Slots | 2 |
Network
| Ethernet LAN | Yes |
| Ethernet Interface Type | 2.5 Gigabit Ethernet |
| Wi-Fi | No |
Rear Panel I/O Ports
| USB 2.0 Type-A | 2 |
| USB 3.2 Gen 1 Type-A | 4 |
| HDMI | 1 |
| Ethernet (RJ-45) | 1 |
Internal I/O Headers
| USB 2.0 Connectors | 2 |
| USB 3.2 Gen 1 Connectors | 2 |
| SATA III Connectors | 4 |
| CPU Fan Connector | Yes |
| Chassis Fan Connectors | 3 |
| ATX Power Connector (24-pin) | Yes |
| EPS Power Connector (8-pin) | Yes |
| 12V Power Connector | Yes |
| Front Panel Audio Connector | Yes |
| Front Panel Connector | Yes |
| RGB LED Header (ARGB) | Yes (3×) |
| TPM Connector | Yes |
| COM Connector | 1 |
| S/PDIF Out Connector | Yes |
Audio
| Audio Output Channels | 7.1 Channels |
BIOS
| BIOS Type | UEFI AMI |
| BIOS Memory Size | 256 Mbit |
Physical
| Width | 244 mm |
| Depth | 221 mm |
| Weight (Board) | 0.83 kg |
Packaging
| Package Width | 270 mm |
| Package Depth | 263 mm |
| Package Height | 51.5 mm |
| Package Weight | 1.02 kg |
| Cables Included | SATA |
| Screws Included | Yes |