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ASUS PRIME B850M-A micro-ATX motherboard with AMD Ryzen 9 9900X CPU in AM5 socket

ASUS

ASUS PRIME B850M-A AMD motherboard & Ryzen 9 9900X CPU combo

SKU CH-XJEZ-QGP9D

B850 micro-ATX motherboard paired with a 12-core, 24-thread Ryzen 9 9900X CPU, supporting DDR5 up to 8000 MT/s, three M.2 slots, PCIe 5.0, and 2.5 Gb Ethernet

  • CPU Socket TypeAM5

Motherboard PRIME B850M-A

Struck-through versions exist but are not stocked here.

CPU + Ryzen 9 9900X

  • 12 cores and 24 threads deliver high multi-task throughput
  • DDR5 memory up to 8000 MT/s overclocked for faster data rates
  • Three M.2 slots provide up to 128 Gbps total bandwidth
  • 5 Gb Ethernet and PCIe 5.0 slot enable high-speed I/O
  • 6 GHz max boost clock gives strong single-thread performance

ASUS PRIME B850M-A with Ryzen 9 9900X

This motherboard and CPU combo pairs an ASUS PRIME B850M-A micro-ATX board with an AMD Ryzen 9 9900X processor. The 12-core, 24-thread chip runs on the Zen 5 architecture and reaches a 5.6 GHz max boost. The board uses the AM5 socket and B850 chipset, targeting builders who want a compact platform for high-end desktop performance. ||

Thermals, noise and power draw

The motherboard uses an 8+2+1 power module layout on a 6-layer PCB with Digi+ VRM digital control. VRM heatsinks and thermal pads handle voltage-regulator heat, while dedicated M.2 heatsinks cool storage. A 4-pin PWM/DC fan header and an integrated water-pump pin give flexible cooling options, letting the system stay quiet under typical loads. ||

Bundled software and accessories

UEFI BIOS provides low-level hardware tuning, while AURA SYNC and a second-generation addressable ARGB header coordinate RGB lighting across compatible parts. Realtek 2.5 Gb Ethernet and front-panel USB 5 Gbps Type-C support are built into the board, so no extra adapters are needed for wired networking or high-speed front I/O.

Highlights

  • 12 cores and 24 threads deliver high multi-task throughput
  • DDR5 memory up to 8000 MT/s overclocked for faster data rates
  • Three M.2 slots provide up to 128 Gbps total bandwidth
  • 5 Gb Ethernet and PCIe 5.0 slot enable high-speed I/O
  • 6 GHz max boost clock gives strong single-thread performance

Specifications

BrandASUS
ModelPRIME B850M-A+R9 9900X
CPU Socket TypeAM5

Other versions of this model

5 more in the same range

Same family, different memory, cooler or clock — compare before you commit.

Questions about this item

How do I install the Ryzen 9 9900X into the AM5 socket and what step is often missed?

Lift the socket lever, align the triangle on the CPU with the socket marker, lower the chip without force, then close and lock the lever; the step many miss is removing the protective plastic cover from the motherboard socket before seating the processor.

What maintenance will the VRM cooling and M.2 heatsinks need over time?

Dust the VRM heatsinks and M.2 heatsinks with compressed air every few months; if thermal pads on the M.2 shields become compressed or dry, replace them with pads of the same thickness to keep temperatures in check.

What limit appears first when the 12-core 24-thread CPU runs at 5.6 GHz boost under sustained load?

The 8+2+1 power modules and VRM heatsinks will hit their thermal ceiling before the CPU reaches its maximum boost duration, so adequate case airflow and a capable cooler are essential to maintain performance.

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