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Rectangular mATX board, matte black PCB, silver AM5 socket, silver heatsinks, two DDR5 slots, two M.2 covers, I/O shield with HDMI

MSI

MSI PRO B840M-B AMD motherboard AM5 socket mATX

SKU CH-AFQF-HTVVV MPN PRO B840M-B

An mATX motherboard for AMD Ryzen 7000, 8000 and 9000 series CPUs with dual-channel DDR5, PCIe 4.0 graphics and dual M.2 slots, 2.5G LAN and four SATA ports

  • ProcessorRyzen 7000 Series / Ryzen 8000 Series / Ryzen 9000 Series
  • ChipsetAMD B840
  • CPU socketAM5
  • Memory slot count2 × 288pin (DDR5)
  • Supported memory2 DIMMs, Dual Channel DDR5 – 8000+ MT/s (OC)
  • Memory channelsDual Channel
  • Supports Ryzen 7000, 8000 and 9000 series processors with AM5 socket
  • Two DDR5 slots reach 8000+ MT/s overclocked for faster memory throughput
  • Dual M.2 slots run at PCIe 4.0 x4 for high-speed storage bandwidth
  • Realtek 8125 2.5G LAN delivers 2.5 Gbps wired network performance
  • EZ PCIe Clip II enables one-finger graphics card release in tight cases

Business mATX AM5 Board

The MSI PRO B840M-B is a micro-ATX motherboard built on the AMD B840 chipset for socket AM5 processors. It accepts Ryzen 7000, 8000 and 9000 series CPUs and provides two DDR5 DIMM slots running dual-channel up to 8000 MT/s when overclocked. The board includes one PCIe 4.0 x16 slot, one PCIe 3.0 x1 slot, four SATA 6Gb/s ports and two M.2 sockets sourced from the CPU that support 2280 and 2260 devices at PCIe 4.0 x4 speeds.

Small-Case Business Builds

This board suits compact business or productivity systems that need current-generation Ryzen performance with 2.5 GbE networking and dual M.2 storage in a small chassis. Builders who require four memory slots, additional PCIe expansion or integrated Wi-Fi should consider a different model because this mATX design provides only two DIMM sockets, a single x16 slot and a wired Realtek 8125 LAN controller only.

Two DDR5 Slots Maximum

The decisive specification is the two-slot DDR5 layout limited to 288-pin modules in dual-channel mode. If the intended system must populate four memory sticks or exceed the capacity ceiling imposed by two slots, this motherboard cannot meet that requirement and a full-size ATX alternative with four DIMM sockets is necessary.

How it compares

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

Price $76.99
Cheaper than about 84% of the 1,906 comparable items (median $224.49).

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Specifications

Product
Brand nameMSI
Model namePRO B840M-B
Part numberPRO B840M-B
Processor
ProcessorRyzen 7000 Series / Ryzen 8000 Series / Ryzen 9000 Series
CPU socketAM5
ChipsetAMD B840
Memory
Memory slot count2 × 288pin (DDR5)
Supported memory2 DIMMs, Dual Channel DDR5 – 8000+ MT/s (OC)
Memory channelsDual Channel
Storage
SATA ports4 x SATA 6Gb/s
M.2 slotsM.2_1 Source (From CPU) supports up to PCIe 4.0 x4 , supports 2280/2260 devices
M.2_2 Source (From CPU) supports up to PCIe 4.0 x4 , supports 2280/2260 devices
M2_2 slot
- Supports up to PCIe 4.0 x4
- Supports up to PCIe 4.0 x2 (For Ryzen 8500/ 8300 Series processors)
Connectivity
Ethernet controllerRealtek 8125 2.5G LAN
Maximum network speed2.5 Gbit/s
Ports & slots
PCIe 4.0 x16 slots1 x PCI Express 4.0 x16
PCIe x1 slots1 x PCIe 3.0 x1 slot
Rear panel ports1x Clear CMOS Button
1x Flash BIOS Button
1x VGA
1x HDMI
1x 2.5G LAN
4x USB 5 Gbit/s Type-A
2x USB 2.0
3x Audio Connectors.
Ethernet port1 x RJ45
Size & build
Shipping weight1.00 kg
Package size279 × 254 × 76 mm

Questions about this item

How loud and hot does the PRO B840M-B get when running all day with a Ryzen 9000 CPU?

Frozr AI Cooling monitors CPU and GPU temperatures and automatically adjusts fan duty cycles through the 2A CPU header and 1A system headers to keep noise and heat in check during sustained loads.

Which components must I already own for this AM5 board to POST?

You need a Ryzen 7000, 8000 or 9000 series processor and two DDR5 DIMMs; the board provides 7-phase direct CPU power, 2-phase SOC power and 1-phase MISC power for them.

Will my older SATA SSDs and PCIe 3.0 add-in card work alongside the new M.2 slots?

Four SATA 6Gb/s ports accept legacy drives, one PCIe 3.0 x1 slot fits older expansion cards, and two CPU-linked M.2 sockets run at PCIe 4.0 x4 for current storage.

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