ASUS PRIME B840M-A-CSM AM5 mATX Motherboard DDR5 B840
ASUS
ASUS PRIME B840M-A-CSM AM5 mATX Motherboard DDR5 B840
The ASUS PRIME B840M-A-CSM is a micro-ATX motherboard built for AMD Ryzen 9000, 8000, and 7000 series processors, offering stable power delivery and extensive memory tuning for builders seeking a compact platform with strong core performance and AI-ready features.
Why this product
8+2+1 phase power design with discrete MOSFETs
Dedicated power stages ensure stable voltage delivery under load, supporting up to 170W AMD processors without thermal stress.
Three M.2 slots with up to 64 Gbps PCIe 4.0
Two PCIe 4.0 slots and one PCIe 3.0 slot accommodate fast NVMe drives across multiple configurations and future storage expansion.
Extensive DDR5 overclocking support
Full AMD EXPO and ASUS Enhanced Memory Profile (AEMP) support unlocks speeds beyond 7600+ MT/s for advanced users and enthusiasts.
Comprehensive thermal management
Dedicated heatsinks on the VRM, M.2 slots, and chipset keep core components within safe operating ranges during sustained workloads.
2.5Gb Ethernet with LANGuard protection
Realtek chipset delivers stable network connectivity with built-in surge protection for the Ethernet port.
- SocketAMD AM5
- ChipsetAMD B840
- Form FactorMicro-ATX
- Memory SupportDDR5, up to 256GB @ 7600+ MT/s (OC)
- M.2 Slots3 (two PCIe 4.0 x4, one PCIe 3.0 x4)
- SATA Ports4 × 6Gb/s
- SKUASU-2639
- EAN4711387797204
- Supports AMD Ryzen 9000, 8000, and 7000 series processors in AM5 socket configuration.
- Accommodates DDR5 memory up to 256GB capacity with dual-channel architecture.
- Fits standard micro-ATX cases (9.6 × 9.6 inches).
- PCIe 4.0 x16 slot operates at x8 or x4 mode on Ryzen 8000 series; full x16 on Ryzen 9000 and 7000 series.
- Does not support Intel processors or older AMD platforms.
- No built-in graphics output for processors without integrated graphics; requires discrete GPU or APU.
Best for
- Compact builds and Small Form Factor (SFF) systems that need full-featured connectivity.
- Ryzen 7000 and 9000 series systems with stable, overclocked DDR5 memory setups.
- Builders prioritising M.2 storage expansion with fast PCIe 4.0 drive support.
- Users requiring AI-ready platform features and advanced BIOS tuning options.
Trade-offs
- High-end enthusiasts requiring extreme VRM capacity or multiple PCIe x16 slots running at full bandwidth simultaneously.
- Budget-conscious builders who do not need DDR5 or advanced overclocking features.
- Workstations requiring more than 7 USB ports (rear + internal expansion) or Thunderbolt connectivity.
- Users with Ryzen 8000 APUs relying on heavy PCIe 4.0 slot bandwidth, as the primary slot drops to x8/x4 mode on that generation.
ASUS Prime series motherboards are expertly engineered to unleash the full potential of AMD Ryzen™ 9000 series processors. The PRIME B840M-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 B840M-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.
Comprehensive memory tuning options are the cornerstone of PRIME motherboards. The PRIME B840M-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 B840M-A-CSM offers extensive AMD Extended Profiles for Overclocking (EXPO™) support and a wide array of UEFI settings for further performance tweaks.
PRIME B840M-A-CSM offers a total of three M.2 slots, including two that support data-transfer speeds of up to 64 Gbps via PCIe 4.0, and one that supports PCIe 3.0.
This motherboard offers a versatile range of connectivity, including support for PCIe 4.0 slot and an arsenal of USB ports which includes Type-C® connections.
General
| Brand | ASUS |
|---|---|
| Model | PRIME B840M-A-CSM |
| Form Factor | Micro-ATX (9.6 × 9.6 inches) |
CPU & Power
| Socket | AMD AM5 |
|---|---|
| Chipset | AMD B840 |
| Supported Processors | AMD Ryzen 9000, 8000, and 7000 series (up to 170W TDP) |
| Power Phases | 8+2+1 digital power design |
Memory & Storage
| Memory Type | DDR5 |
|---|---|
| Memory Channels | Dual channel |
| Maximum Capacity | 256GB |
| Memory Speed Support | Up to 7600+ MT/s (OC) with EXPO and AEMP |
| M.2 Slots | 3 (M.2_1: 2280 PCIe 4.0 x4; M.2_2: 2242/2260/2280 PCIe 4.0 x4; M.2_3: 2280 PCIe 3.0 x4) |
| SATA Ports | 4 × SATA 6Gb/s |
Expansion & Connectivity
| PCIe Slots | 1 × PCIe 4.0 x16 (x16 on Ryzen 9000/7000, x8/x4 on Ryzen 8000); 2 × PCIe 3.0 x16 (x1 mode) |
|---|---|
| Rear USB Ports | 2 × USB 10Gbps Type-A, 1 × USB 5Gbps Type-C, 4 × USB 2.0 Type-A |
| Front USB Headers | 1 × USB 5Gbps Type-C connector, 1 × USB 5Gbps header (supports 2 ports), 2 × USB 2.0 headers (supports 4 ports) |
| Ethernet | 1 × Realtek 2.5Gb with LANGuard protection |
| Video Outputs | 2 × DisplayPort 1.4 (8K@30Hz), 1 × HDMI 2.1 (4K@60Hz) |
Audio & Software
| Audio Codec | Realtek 7.1 Surround Sound (24-bit/192 kHz) |
|---|---|
| RGB Lighting | 3 × Addressable Gen 2 headers with Aura Sync |
| BIOS | 256 Mb Flash ROM, UEFI AMI BIOS |
| Software Suite | Armoury Crate, Aura Creator, Fan Xpert 2+, ASUS DriverHub, TurboV Core |
Protection & Cooling
| VRM Protection | DIGI+ VRM, Overvoltage protection |
|---|---|
| Expansion Slot Protection | SafeSlot Core+ |
| Heatsinks | VRM heatsink, M.2 heatsink, Chipset heatsink |
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.