Asus Prime B840M-A WiFi AMD AM5

Description

ASUS Prime Engineering in a Micro-ATX Footprint

The Prime B840M-A WiFi brings the same ASUS Prime DNA found on the ATX B840-Plus WiFi into a 244 mm × 244 mm Micro-ATX form factor, making it a strong option for compact builds where ATX clearance isn’t available but no meaningful compromise on feature set is wanted. The 8+2+1 phase power design with discrete MOSFETs and DIGI+ VRM provides stable, efficient power delivery for the full Ryzen 7000/8000/9000 lineup up to 170W TDP. A single 8-pin ATX12V connector handles CPU power — clean, simple, and compatible with virtually any modern PSU. The VRM heatsink, SafeSlot reinforced primary PCIe slot, stainless steel I/O panel, premium audio capacitors with dedicated PCB layers, and audio shielding all carry over from the ATX sibling without compromise.

⚠️ The B840 chipset does not support CPU overclocking. Memory overclocking via AMD EXPO and ASUS AEMP profiles is supported up to DDR5-7600+ (OC). If CPU OC headroom is a requirement, B850 is the next step up.

⚠️ The 8+2+1 discrete MOSFET VRM is best matched to 65–105W TDP processors for sustained workloads. 170W-rated CPUs are supported at stock but represent the upper comfort boundary for this power stage.

Memory and Storage

Four DDR5 DIMM slots support dual-channel operation up to 256 GB with AMD EXPO and ASUS AEMP profile support, reaching DDR5-7600+ (OC). Storage across three M.2 slots is well distributed: M2_1 is CPU-connected at PCIe 4.0 x4 (64 Gb/s) in 2280 form factor, M2_2 is also CPU-connected at PCIe 4.0 x4 (64 Gb/s) and notably supports shorter 2242 and 2260 drives in addition to 2280 — useful for smaller drives or repurposed laptop SSDs. M2_3 is chipset-connected at PCIe 3.0 x4 (32 Gb/s) and supports standard 2280 only. All three slots include M.2 heatsink coverage. Four SATA 6Gb/s ports are available for traditional drives, and RAID support follows the same CPU-generation-dependent pattern as the B840-Plus: RAID 0/1/5/10 on Ryzen 9000, RAID 0/1/10 on Ryzen 7000, and RAID 0/1 only on Ryzen 8000.

⚠️ M2_2 drops from PCIe 4.0 x4 to x2 with Ryzen 8000 Phoenix 2 processors. Ryzen 7000 and 9000 CPUs run both CPU-connected M.2 slots at the full PCIe 4.0 x4 rate.

⚠️ No PCIe Gen5 M.2 slot is present — the fastest M.2 tier is PCIe 4.0 x4 (64 Gb/s). If Gen5 NVMe is a priority, a B850 or X870 board is required.

Connectivity and I/O

The rear I/O panel offers a notably strong display output for a Micro-ATX board at this tier: dual DisplayPort 1.4 (up to 8K 30Hz each) plus HDMI 2.1 (4K 60Hz) covers triple-display iGPU setups for Ryzen 8000 G-series builds. Rear USB consists of two USB 10 Gbps Type-A and four USB 2.0 Type-A ports, with a USB 5 Gbps Type-C port also on the rear — seven rear ports total. Front panel USB is well covered with a USB 5 Gbps Type-C header plus a standard USB 5 Gbps header supporting two additional ports. Wi-Fi 6E (802.11ax, 2.4/5/6 GHz, 2×2 MU-MIMO) and Bluetooth 5.3 are onboard, with Realtek 2.5G LANGuard Ethernet for wired connectivity. Fan headers include one CPU fan, one CPU OPT, one AIO pump, and three chassis fan headers. Three Addressable Gen 2 (ARGB) headers provide Aura Sync lighting control. Additional internal headers include S/PDIF out, COM port, SPI TPM, and a Clear CMOS header.

⚠️ The primary PCIe 4.0 x16 GPU slot drops to x8/x4 mode with Ryzen 8000 Series processors. The two chipset-side PCIe 3.0 x16 slots run at x1 mode only — suitable for network cards, capture cards, and similar low-bandwidth add-ins, not additional GPUs.

⚠️ Integrated display output (HDMI and DisplayPort) requires a Ryzen processor with integrated Radeon graphics. Non-G Ryzen 7000/9000 CPUs do not include an iGPU — a discrete GPU is required in those builds.

Key Highlights

• AMD B840 chipset, Socket AM5
• Supports Ryzen 7000, 8000, and 9000 Series, up to 170W TDP
• Micro-ATX form factor — 244 mm × 244 mm
• 8+2+1 phase power design, discrete MOSFETs, DIGI+ VRM
• Single 8-pin ATX12V CPU power connector
• 4× DDR5 DIMM slots, dual-channel, up to 256 GB, DDR5 7600+ (OC)
• AMD EXPO and ASUS AEMP memory profile support
• 1× M.2 PCIe 4.0 x4 (CPU, 64 Gb/s, 2280) — M2_1, with heatsink
• 1× M.2 PCIe 4.0 x4 (CPU, 64 Gb/s, 2242/2260/2280) — M2_2, with heatsink
• 1× M.2 PCIe 3.0 x4 (chipset, 32 Gb/s, 2280) — M2_3, with heatsink
• 4× SATA 6Gb/s ports
• RAID 0/1/5/10 (Ryzen 9000) / 0/1/10 (Ryzen 7000) / 0/1 (Ryzen 8000)
• 1× PCIe 4.0 x16 (primary GPU, SafeSlot Core+) + 2× PCIe 3.0 x16 (x1 mode, chipset)
• Dual DisplayPort 1.4 (up to 8K 30Hz each) + HDMI 2.1 (4K 60Hz) — rear
• Realtek 2.5G Ethernet with ASUS LANGuard
• Wi-Fi 6E (802.11ax, 2.4/5/6 GHz, 2×2 MU-MIMO) + Bluetooth 5.3
• 2× rear USB 10 Gbps Type-A + 1× rear USB 5 Gbps Type-C + 4× USB 2.0 Type-A
• Front USB 5 Gbps Type-C header + 5 Gbps header (2 ports)
• 1× CPU fan + 1× CPU OPT + 1× AIO pump + 3× chassis fan headers
• 3× Addressable Gen 2 (ARGB) headers — Aura Sync compatible
• S/PDIF out header, SPI TPM header, COM port header
• BIOS FlashBack button (no CPU/RAM required)
• ASUS Q-LED Core debug LEDs (CPU/DRAM/VGA/BOOT)
• ASUS 5X Protection III (overvoltage protection, SafeSlot Core+, stainless steel I/O)
• No PCIe Gen5 M.2 — top M.2 speed is PCIe 4.0 x4

 

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