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Micro-ATX motherboard in dark finish with CPU installed, silver VRM heatsinks, three M.2 covers and rear I/O panel visible

ASUS

ASUS PRIME B850M-A & Ryzen 9 9900X3D Combo AMD motherboard

SKU CH-Q73H-3VF63

Micro-ATX AM5 motherboard paired with a 12-core Ryzen 9 9900X3D CPU featuring 128 MB L3 cache, DDR5 8000 MT/s support, PCIe 5.0 slot, three M.2 slots, 2.5 Gb Ethernet and front USB 5 Gbps Type-C

  • CPU socketAM5

Motherboard PRIME B850M-A

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CPU + Ryzen 9 9900X3D

  • Ready-to-build combo with matched Ryzen 9 9900X3D CPU and PRIME B850M-A board
  • Stable power delivery from 8+2+1 phase VRM on six-layer PCB with digital control
  • DDR5 memory overclock headroom to 8000 MT/s plus three M.2 slots for fast storage
  • Comprehensive cooling with VRM heatsinks, M.2 heatsinks, water-pump header and PWM fan headers
  • PCIe 5.0 slot, 2.5 Gb Ethernet, front USB 5 Gbps Type-C and dual DisplayPort outputs

AM5 motherboard and Ryzen 9 9900X3D bundle

This combo pairs an ASUS PRIME B850M-A micro-ATX board with an AMD Ryzen 9 9900X3D processor. The CPU delivers 12 cores built on TSMC 4nm FinFET Granite Ridge architecture with a 120W TDP. Integrated AMD Radeon graphics provide display output without a discrete card. The package targets builders who want a matched platform for gaming or content creation.

Ideal for compact DDR5 systems with high cache needs

The board supports DDR5 memory up to 8000 MT/s when overclocked and offers three M.2 slots for fast storage. A 2.5 Gb Ethernet port and front-panel USB 5 Gbps Type-C header cover modern connectivity. Builders needing more than three M.2 drives or a full-size ATX layout should look at larger boards.

128 MB L3 cache drives gaming responsiveness

The processor includes 128 MB of L3 cache alongside 12 MB of L2 cache. This large cache pool reduces latency in cache-sensitive titles and workloads. If your software benefits more from core count than cache size, a different CPU may suit you better.

How it compares

Measured against everything we stock in Motherboards for AMD CPUs, at today’s prices. Recalculated every night.

Price $930.99
Pricier than about 85% of the 1,906 comparable items (median $224.49).

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Specifications

Product
Brand nameASUS
Model namePRIME B850M-A+R9 9900 × 3D
Processor
CPU socketAM5

Other versions of this model

5 more in the same range

Questions about this item

What size case and CPU cooler clearance does the micro-ATX PRIME B850M-A need?

The board uses the micro-ATX form factor, so it fits any case that accepts micro-ATX or larger. The AM5 socket keeps the same mounting holes as AM4, so existing AM4 coolers will bolt on, but check the cooler's own height limit against your case.

Which BIOS step is required before the Ryzen 9 9900X3D will post on this B850 board?

Update the UEFI BIOS to the latest version that supports Granite Ridge CPUs before installing the processor; without that update the system will not boot.

When should the thermal paste on the 120W Ryzen 9 9900X3D be replaced?

Reapply paste whenever the cooler is removed or if temperatures climb noticeably after a year or two of heavy loads; the 120 W TDP makes consistent contact important.

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