MSI B850M Mortar Wi-Fi Review: Revolutionary mATX Board With Back M.2 Slot

Compact motherboard offering advanced connectivity, strong VRM design, and a rare rear-mounted M.2 slot configuration

Hardware by Nakiro on Nov 28, 2025

The MSI B850M Mortar Wi-Fi is one of the most requested mATX motherboards since the channel began. It is designed for Ryzen 7000, 8000, and 9000 processors and features a range of unique features that set it apart from other compact motherboards.

One of the most notable aspects of this motherboard is an m.2 slot on the back—a feature rarely seen on mATX boards.

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Accessories

Included with the motherboard are the Wi-Fi antenna for built-in Wi-Fi 7 and Bluetooth 5.4, documentation, stickers, a quick installation guide, regulatory notices, and the standard accessories found with most MSI motherboards.

There is also a single SATA cable for connecting a 2.5-inch SSD or a 3.5-inch hard drive, and an easy connector that combines all front-panel cables into a single block, simplifying installation and cable management. Additionally, there is a combined PWM and 3-pin 5V addressable RGB cable that connects to a specific header on the board for easier RGB and fan control.

Layout and Features

The front of the B850M Mortar Wi-Fi includes multiple headers for audio, RGB, and fans. These include a front-panel audio header, a 4-pin 12V RGB header, a 3-pin 5V addressable RGB header, a PWM fan header, and an easy-connect header. The board also has a separate PCIe power connector, USB 2.0 front-panel headers for liquid coolers and RGB controllers, a USB 3.2 (10GB) front-panel header, a USB Type-C (20GB) front-panel header, and four right-angled SATA ports for storage.

The 24-pin power connector powers the motherboard, while the diagnostic postcode LED array helps identify system issues. Additional PWM fan headers are located along the edges of the board. At the top left, two 8-pin EPS power connectors provide power to the CPU. PCIe options include a single PCIe 5.0 x16 slot and a PCIe 4.0 x4 slot.

Notably, the PCIe slots have an open-ended design, allowing for additional GPUs even if full bandwidth is not required, which is ideal for AI or computational applications.

VRM and Cooling

The motherboard's digital VRM architecture features 12+2+1 phases, and the smart power stages can handle up to 80A. The IO cover features a large heatsink to help cool the VRM, and a heatsink at the top of the board helps spread heat more quickly.

Socket and RAM Support

The AM5 socket works with Ryzen 7000 to Ryzen 9000 processors, including all X3D versions. The motherboard supports up to 256GB of DDR5 memory at up to 8400 MT/s. This is a manufacturer-imposed restriction, not a recommendation.

M.2 Slots and Storage

The B850M Mortar Wi-Fi has a unique approach to M.2 storage. There are two PCIe Gen5 M.2 slots on the front with quick-release heatsinks that allow tool-less installation. On the back, there is an additional PCIe Gen4x2 M.2 slot, a rare feature for mATX boards.

This back M.2 slot makes installation and maintenance easier without removing a GPU, especially when the top PCIe slot is occupied by a large graphics card.

Rear I/O

The rear I/O includes a clear CMOS button, BIOS flashback button, HDMI 2.1 port, 5Gb Ethernet, three 10GB USB Type-A ports, a 10GB USB Type-C port, four 5Gb USB Type-A ports, and a 20GB USB Type-C port. The board also has Wi-Fi 7 and Bluetooth 5.4 antenna connectors, as well as line-in, line-out, and optical S/PDIF audio outputs.

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Practical Advantages

Having an M.2 slot on the back of an mATX board is particularly advantageous for those installing large GPUs, as it eliminates the need to remove the GPU to access storage drives.

This design choice anticipates trends in motherboard and case design, with many modern cases now featuring large cutouts on the back for easier access.

Connectivity and Networking

The motherboard includes 5Gb Ethernet, which is becoming more common on MSI boards. While multi-gig switches can be expensive, affordable 2.5Gb and higher-speed solutions are available, making this a practical choice for high-speed networking.

Pricing and Availability

Currently, MSI has only listed the product page for the B850M Mortar Wi-Fi. There isn't a set price yet, but a rough estimate of a competitive price might be around $179, based on the features and how it compares to earlier models like the B860M Mortar Wi-Fi, which costs approximately $189. Availability and exact costs have not yet been confirmed.

The MSI B850M Mortar Wi-Fi is a modern mATX motherboard with a rear M.2 slot, a strong VRM design, support for high-speed memory, and several PCIe options. This motherboard is an intriguing choice for people who want to build small systems that work well and make storage easy to access.

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