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Green rectangular micro-ATX board with silver heatsinks, black PCB, rear I/O shield and M.2 covers

ASUS

ASUS PRIME B840M-A WIFI-CSM 90MB1J20-MVAAYC AMD motherboard

SKU CH-X15P-NRPS5 MPN 90MB1J20-MVAAYC

Micro-ATX AM5 board with DDR5 support to 7600 MT/s, three M.2 slots, Wi-Fi 6E and 2.5Gb Ethernet for Ryzen 7000, 8000 and 9000 series CPUs

  • ProcessorRyzen 7000 Series / Ryzen 8000 Series / Ryzen 9000 Series
  • ChipsetAMD B840
  • Form factorMicro ATX
  • CPU socketAM5
  • Memory slot count4 × 288pin (DDR5)
  • Supported memoryUp to 7600+MT/s (OC)

Model PRIME B840M-A WIFI-CSM

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  • Ready for Ryzen 9000, 8000 and 7000 series processors on AM5 socket
  • Four DDR5 slots support up to 192 GB at 7600 MT/s with AMD EXPO
  • Three M.2 slots at PCIe 4.0 x4 plus four SATA 6 Gb/s ports
  • Wi-Fi 6E and Realtek 2.5Gb Ethernet for fast wired and wireless links
  • CSM programme plus 6-layer PCB, alloy chokes and durable capacitors for long-term stability

ASUS PRIME B840M-A WIFI-CSM AM5 Motherboard

The ASUS PRIME B840M-A WIFI-CSM is a Micro ATX motherboard built on the AMD B840 chipset for Socket AM5 processors. It supports Ryzen 7000, 8000 and 9000 series CPUs and provides four DDR5 memory slots with a maximum capacity of 192 GB. The board includes Wi-Fi 6E, 2.5Gb LAN and rear USB 5Gbps Type-C connectivity for modern peripheral support.

Suited to compact AI-ready builds.

This board suits builders who want a compact AM5 platform with three M.2 slots, PCIe 4.0 graphics support and corporate-stable firmware for long-term deployments. The single PCIe 4.0 x16 slot and two chipset x1 slots limit multi-GPU configurations, so users planning multiple graphics cards should look at ATX chipsets with more full-length slots.

Three M.2 slots define storage flexibility

The deciding specification is the trio of M.2 slots: one CPU-attached 2280 slot running at PCIe 4.0 x4, a second CPU-attached slot accepting 2242, 2260 or 2280 drives at PCIe 4.0 x4, and a third chipset-attached 2280 slot. This layout determines how many high-speed drives can be installed directly on the motherboard.

How it compares

Measured against everything we stock in Motherboards for AMD CPUs, at today’s prices. Recalculated every night.

Price $130.99
Cheaper than about 67% of the 1,906 comparable items (median $224.49).

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Specifications

Product
Brand nameASUS
Model namePRIME B840M-A WIFI-CSM
Part number90MB1J20-MVAAYC
Processor
ProcessorRyzen 7000 Series / Ryzen 8000 Series / Ryzen 9000 Series
CPU socketAM5
ChipsetAMD B840
Memory
Memory slot count4 × 288pin (DDR5)
Supported memoryUp to 7600+MT/s (OC)
Max supported RAM192 GB
Memory channelsDual Channel
Memory profilesAMD EXPO
ECC supportYes
BufferingUn-buffered
Storage
SATA ports4 x SATA 6Gb/s
M.2 slotsAMD Ryzen 9000 & 8000 & 7000 Series Desktop Processors
M.2_1 slot (Key M), type 2280 (supports PCIe 4.0 x4 mode)
M.2_2 slot (Key M), type 2242/2260/2280 (supports PCIe 4.0 x4 mode)
AMD B840 Chipset
M.2_3 slot (Key M), type 2280 (supports PCIe 3.0 x4 mode)
SATA and RAID supportAMD RAIDXpert2 Technology supports both PCIe RAID 0/1/5/10 and SATA RAID 0/1/5/10.
*RAID 5 Function is only supported by AMD Ryzen 9000 series CPU.
Audio & video
Sound channelsRealtek 7.1 Surround Sound High Definition Audio CODEC*
- Supports: Jack-detection, Multi-streaming, Front Panel Jack-retasking
- Supports up to 24-Bit/192 kHz playback
Audio Features
- Audio Shielding
- Premium audio capacitors
- Dedicated audio PCB layers
* A chassis with an HD audio module in the front panel is required to support 7.1 Surround Sound audio output.
Connectivity
Maximum network speed2.5 Gbit/s
Wi-Fi standardWi-Fi 802.11 ax
Bluetooth support5.3
Ports & slots
PCIe 4.0 x16 slotsAMD Ryzen 9000 & 7000 Series Desktop Processors*
1 x PCIe 4.0 x16 slot (supports x16 mode)
AMD Ryzen 8000 Series Desktop Processors
1 x PCIe 4.0 x16 slot (supports x8/x4 mode)
PCIe 3.0 x16 slotsAMD B840 Chipset
2 x PCIe 3.0 x16 slots (support x1 mode)
Onboard USB headers1 x USB 5 Gbit/s connector (supports USB Type-C)
1 x USB 5 Gbit/s header supports 2 additional USB 5 Gbit/s ports
2 x USB 2.0 headers support 4 additional USB 2.0 ports
Power
Power connectors1 × 24-pin Main Power connector
1 × 8-pin +12 V CPU Power connector
Size & build
Form factorMicro ATX
Width and length9.6 in × 9.6 in
Shipping weight1.13 kg
Package size279 × 279 × 76 mm
Compatibility
Windows 11 supportWindows 11, Windows 10 64-bit
In the box
In the boxCables
2 x SATA 6Gb/s cables
Miscellaneous
1 x ASUS WiFi Q-Antenna
1 x M.2 rubber package
3 x Screw packages for M.2 SSD
Documentation
1 x Quick start guide
More details
BIOS256 Mb Flash ROM, UEFI AMI BIOS

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