Asus Prime B850M-K AMD AM5

Description

B850’s Key Upgrades in the Most Compact Package

The Prime B850M-K is ASUS’s entry point into the B850 chipset, and it earns its place by delivering the two most meaningful upgrades B850 brings over B840: CPU overclocking support and a PCIe 5.0 x16 primary GPU slot (with Ryzen 7000/9000). Packaged into a slightly narrower Micro-ATX footprint at 244 mm × 221 mm — smaller than the standard 244 mm × 244 mm Micro-ATX size — it fits chassis with tighter board clearances while retaining the core ASUS Prime build quality standards: DIGI+ VRM, LANGuard, SafeSlot reinforced primary PCIe slot, audio shielding with premium capacitors and dedicated PCB layers, stainless steel rear I/O, and a VRM heatsink. The 8+2+1 phase discrete MOSFET power stage handles the mainstream Ryzen range cleanly within its rated 170W CPU envelope, with a single 8-pin ATX12V connector keeping power delivery simple.

⚠️ CPU overclocking is supported on B850. However, the 8+2+1 discrete MOSFET power stage is best matched to 65–105W TDP processors for sustained workloads. Higher-wattage Ryzen 9 chips at stock are within spec, but extended all-core overclocking on 170W processors pushes this VRM to its limits. Ensure good case airflow over the VRM area for any OC workloads.

Memory and Storage

Two DDR5 DIMM slots support dual-channel operation up to 128 GB, with EXPO and ASUS AEMP profiles enabling DDR5-8200+ (OC) on Ryzen 9000, DDR5-9600+ (OC) on Ryzen 8000, and DDR5-8000+ (OC) on Ryzen 7000 — the Ryzen 8000 OC ceiling is notably higher here than on B840 boards. M2_1 is a CPU-connected PCIe 5.0 x4 slot (128 Gb/s) with an M.2 heatsink, delivering full Gen5 NVMe speeds with Ryzen 7000 and 9000 CPUs. M2_2 is a CPU-connected PCIe 4.0 x4 slot (64 Gb/s) supporting 2242, 2260, and 2280 form factors, also with heatsink coverage. There is no third M.2 slot — chipset-connected M.2 storage is absent on this board. Four SATA 6Gb/s ports cover traditional drives. RAID support is CPU-generation dependent: RAID 0/1/5/10 on Ryzen 9000, RAID 0/1/10 on Ryzen 7000, and RAID 0/1 only on Ryzen 8000.

⚠️ Only two M.2 slots are present — there is no chipset-connected third M.2 slot. Builds requiring three or more M.2 drives will need to use SATA SSDs for the additional slots, or step up to a board with a third M.2 slot such as the B840M-A or B850M-A WiFi.

⚠️ M2_1 runs at PCIe 5.0 x4 with Ryzen 7000 and 9000, but drops to PCIe 4.0 x4 with all Ryzen 8000 variants. M2_2 drops from PCIe 4.0 x4 to x2 with Ryzen 8000 Phoenix 2 processors.

Connectivity and I/O

Rear I/O is clean and practical: two USB 10 Gbps Type-A and two USB 5 Gbps Type-A ports sit alongside four USB 2.0 Type-A ports — eight rear USB ports total, all Type-A with no rear Type-C. DisplayPort 1.4 (up to 8K 30Hz) and HDMI 2.1 (4K 60Hz) serve iGPU-equipped processors. A legacy PS/2 keyboard/mouse combo port is present on the rear for enterprise and legacy peripheral users. Realtek 2.5G LANGuard Ethernet handles wired networking, and BIOS FlashBack enables firmware updates without CPU or RAM installed. Front panel USB is handled by a USB 5 Gbps Type-C header and a standard 5 Gbps header for two additional ports. Fan headers consist of one CPU fan header and three chassis fan headers — no CPU OPT or AIO pump header. Three Addressable Gen 2 (ARGB) headers support Aura Sync RGB. Additional internal headers include S/PDIF out, COM port, and SPI TPM.

⚠️ No Wi-Fi is onboard — this is a wired-only board with no M.2 Key E slot for a wireless module. A USB or PCIe Wi-Fi adapter will be needed if wireless connectivity is required.

⚠️ No AIO pump header or CPU OPT header is present — just a single CPU_FAN1 and three chassis fan headers. AIO cooler pump cables can be connected to a chassis fan header, but these are typically limited to lower current ratings than a dedicated pump header. Verify your AIO cooler is compatible with this configuration.

⚠️ Integrated display output (HDMI/DisplayPort) requires a Ryzen processor with integrated Radeon graphics. Non-G Ryzen 7000/9000 CPUs do not include an iGPU — a discrete GPU is required in those builds.

Key Highlights

• AMD B850 chipset, Socket AM5 — CPU overclocking supported
• Supports Ryzen 7000, 8000, and 9000 Series, up to 170W TDP
• Compact Micro-ATX form factor — 244 mm × 221 mm
• 8+2+1 phase power design, discrete MOSFETs, DIGI+ VRM
• Single 8-pin ATX12V CPU power connector
• 2× DDR5 DIMM slots, dual-channel, up to 128 GB
  DDR5-8200+ (OC, Ryzen 9000) / 9600+ (OC, Ryzen 8000) / 8000+ (OC, Ryzen 7000)
• AMD EXPO and ASUS AEMP memory profile support
• 1× M.2 PCIe 5.0 x4 (CPU, 128 Gb/s, 2280, with heatsink) — M2_1
• 1× M.2 PCIe 4.0 x4 (CPU, 64 Gb/s, 2242/2260/2280, with heatsink) — M2_2
• No third M.2 slot
• 4× SATA 6Gb/s ports
• RAID 0/1/5/10 (Ryzen 9000) / 0/1/10 (Ryzen 7000) / 0/1 (Ryzen 8000)
• 1× PCIe 5.0 x16 (primary GPU, SafeSlot, Ryzen 7000/9000) / PCIe 4.0 x8/x4 (Ryzen 8000)
• 1× PCIe 4.0 x16 slot (chipset, x4 mode)
• DisplayPort 1.4 (up to 8K 30Hz) + HDMI 2.1 (4K 60Hz) — rear
• Realtek 2.5G Ethernet with ASUS LANGuard
• No onboard Wi-Fi — wired-only, no M.2 Key E slot
• 2× rear USB 10 Gbps Type-A + 2× USB 5 Gbps Type-A + 4× USB 2.0 Type-A
• PS/2 keyboard/mouse combo port — rear
• Front USB 5 Gbps Type-C header + 5 Gbps header (2 ports)
• 1× CPU fan + 3× chassis fan headers (no AIO pump, no CPU OPT header)
• 3× Addressable Gen 2 (ARGB) headers — Aura Sync compatible
• S/PDIF out header, SPI TPM header, COM port header
• BIOS FlashBack button (no CPU/RAM required)
• ASUS Q-LED Core debug LEDs (CPU/DRAM/VGA/BOOT)
• ASUS 5X Protection III (overvoltage protection, SafeSlot, stainless steel I/O)

 

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