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Product Overview

The Asus PRIME B850M-A-CSM motherboard is a micro ATX board for Socket AM5 built on the AMD B850 chipset, supporting Ryzen 7000, 8000 and 9000 series processors. It offers four DDR5 slots for up to 256 GB of memory at speeds up to DDR5-8000+ (OP), one PCIe 5.0 x16 slot, three M.2 slots, 2.5 Gigabit Ethernet and an 8+2+1 phase power design with discrete MOSFETs.

This board suits compact AM5 builds where you want PCIe 5.0 for the graphics card and fast NVMe storage without paying for a full ATX layout. With seven 4-pin PWM fan headers, three addressable RGB headers, four SATA ports and a mix of USB 3.2 Gen 2, Gen 1 and USB 2.0 ports, it covers everyday gaming and general-purpose PC use. It belongs to Asus’s Corporate Stable Model range, which offers up to 36 months of product lifecycle support. A BIOS update may be required for the newest processors.

Specification

• Manufacturer: Asus
• Model: PRIME B850M-A-CSM
• MPN: 90MB1LQ0-M0EAYC
• EAN: 4711636054706
• CPU socket: AMD Socket AM5
• Chipset: AMD B850
• Form factor: micro ATX
• Memory: 4x DDR5 DIMM, dual-channel, up to 256 GB, up to DDR5-8000+ (OP), ECC and non-ECC
• PCIe slots: 1x PCIe 5.0 x16, 1x PCIe 4.0 x16 (x4 lanes), 1x PCIe x1
• M.2 slots: 3x M.2 (M key), PCIe, 2280 – first slot PCIe 5.0, others PCIe 4.0
• SATA: 4x SATA III, RAID 0/1/5/10
• Networking: Realtek 2.5 Gigabit Ethernet, no Wi-Fi
• Rear USB: 2x USB-A 3.2 Gen 2 (10 Gbit/s), 2x USB-A 3.2 Gen 1 (5 Gbit/s), 4x USB-A 2.0
• Video outputs: 1x HDMI 2.1, 2x DisplayPort 1.4 (requires CPU with integrated graphics)
• Audio: Realtek 7.1 channel codec
• Power connectors: 24-pin ATX + 2x 8-pin EPS
• Fan and RGB headers: 7x 4-pin PWM fan headers, 3x addressable RGB headers
• Dimensions (W x D): 244 x 244 mm

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