ASUS Prime B550M-A AC Motherboard: AM4, PCIe 4.0, WiFi and what it offers

The ASUS Prime B550M-A AC is a Micro ATX motherboard for AMD's AM4 socket. It is built around 3rd Gen Ryzen processors and adds PCIe 4.0, built-in WiFi and dual M.2 slots. ASUS aims it at mainstream users and DIY builders who want a compact, general-purpose foundation for a desktop PC.

Socket, chipset and form factor

AM4 is the socket used by a long line of Ryzen processors, and the B550 chipset is the mainstream chipset that brought PCIe 4.0 to that platform. ASUS lists this board as made for 3rd Gen Ryzen. Before buying, check the manufacturer's CPU support list for the exact processor you plan to use, because support for other generations typically depends on the BIOS version.

Micro ATX is a smaller board than full ATX, at roughly 10 x 10 inches (about 25 x 25 cm) here. It fits in Micro ATX cases and in most larger ATX cases, but it has fewer expansion slots than a full-size board.

What PCIe 4.0 means in practice

PCIe 4.0 doubles the per-lane data rate of PCIe 3.0. The board has one PCIe 4.0 x16 SafeSlot for a graphics card, and ASUS says one of its two M.2 slots runs at PCIe 4.0 x4 for an NVMe SSD. A drive built for PCIe 4.0 can then reach faster sequential speeds than one limited to PCIe 3.0, although everyday tasks often feel similar. The second M.2 slot gives you room for another drive.

Connectivity

The board includes WiFi, 1Gb wired LAN, USB 3.2 Gen 2 Type-A and a set of video outputs: HDMI 2.1 (4K at 60Hz), D-Sub and DVI. Video outputs on a motherboard are used only with processors that have integrated graphics, so check whether your chosen Ryzen model includes them. ASUS also notes support for ECC memory, which typically needs a compatible processor and memory modules to take effect.

Cooling and memory

The board carries a VRM heatsink and a PCH heatsink, plus hybrid fan headers and the Fan Xpert 2 utility for adjusting fan behaviour. The heatsinks help keep the power delivery and chipset cooler under load. ASUS also describes OptiMem, a proprietary memory trace layout that it says lets memory kits run at higher frequencies with lower voltages.

Protection features

ASUS groups its safeguards under the name 5X Protection III. It includes LANGuard, DRAM overcurrent protection, overvoltage protection, SafeSlot Core protection and a stainless-steel back I/O panel. These are designed to guard the board against electrical surges and the stress of heavy graphics cards.

Lighting

An addressable Gen 2 RGB header and Aura Sync support let you connect compatible lighting strips and coordinate them with other Aura-ready parts, if you want a lit build.

What to check before you buy

• Confirm your processor is on the board's CPU support list, and whether a BIOS update is needed.
• Make sure your case supports Micro ATX.
• Check the memory type and speeds the board supports, and the number of RAM slots.
• Count your drives: the board has two M.2 slots, only one at PCIe 4.0 x4.
• Verify the video outputs match your monitor, and that your CPU has integrated graphics if you plan to use them.
• Check what is in the box, such as the WiFi antenna and cables.

The short version

• Micro ATX board for AM4 and 3rd Gen Ryzen processors.
• One PCIe 4.0 x16 slot and dual M.2 slots, one at PCIe 4.0 x4.
• WiFi, 1Gb LAN, USB 3.2 Gen 2 and HDMI 2.1, D-Sub and DVI outputs.
• VRM and PCH heatsinks, hybrid fan headers and 5X Protection III.

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