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ATX motherboard with AM5 socket CPU installed, dark PCB with silver heatsinks

ASUS

ASUS PRIME B850-PLUS & Ryzen 9 9900X AMD motherboard combo

SKU CH-HMDX-KMMS9

An AM5 motherboard and 12-core, 24-thread Ryzen 9 9900X CPU combo with 12+2 phase power, DDR5 optimisation, one PCIe 5.0 and two PCIe 4.0 M.2 slots, plus 2.5 Gb Ethernet

  • CPU socketAM5

Motherboard PRIME B850-PLUS

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CPU + R9 9900X

  • 12-core 24-thread Ryzen 9 9900X delivers high multi-tasking throughput
  • 12+2 phase Digi+ VRM supplies stable power for Ryzen 9000/8000/7000 CPUs
  • AEMP boosts DDR5-5600 speeds and tightens timings on non-EXPO kits
  • One PCIe 5.0 x4 M.2 slot at 128 Gbps plus two PCIe 4.0 x4 slots for fast storage
  • 5Gb Ethernet with LANGuard gives faster, more reliable wired networking

Motherboard & CPU Combo

This bundle pairs the ASUS PRIME B850-PLUS motherboard with the AMD Ryzen 9 9900X processor for Socket AM5. The combination targets enthusiasts building a high-performance desktop around the Zen 5 architecture and DDR5 memory.

DIY-Friendly Installation

A pre-mounted I/O shield simplifies motherboard placement in the chassis. Fan Xpert 2+ provides granular cooling control, while Aura Sync addressable Gen 2 headers let you coordinate RGB lighting without extra adapters.

Capacity & Headroom

The 12-core, 24-thread CPU reaches a 5.6 GHz max boost with 64 MB L3 cache and supports DDR5-5600. Storage headroom comes from one PCIe 5.0 x4 M.2 slot (up to 128 Gbps) plus two PCIe 4.0 x4 slots, while 2.5 Gb Ethernet handles wired networking.

How it compares

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

Price $768.99
Pricier than about 77% of the 1,906 comparable items (median $224.49).

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Specifications

Product
Brand nameASUS
Model namePRIME B850-PLUS+R9 9900X
Processor
CPU socketAM5

Other versions of this model

5 more in the same range

Questions about this item

How do I verify the 12+2 phase VRM is delivering stable power to the Ryzen 9 9900X after build completion?

Enter the UEFI and monitor the CPU Vcore and VRM temperature readings under load; steady voltages and controlled thermals confirm the Digi+ VRM is operating as designed for the 12-core processor.

The combo lists a pre-mounted I/O shield — which other components must I purchase separately to finish the system?

You still need DDR5 memory modules, a CPU cooler compatible with AM5, storage drives for the three M.2 slots, a graphics card, a power supply, and a chassis.

The board offers one PCIe 5.0 x4 M.2 slot and two PCIe 4.0 x4 slots — which should I use for the primary OS drive?

Install the OS on the PCIe 5.0 x4 M.2 slot to utilise the full 128 Gbps bandwidth; reserve the two PCIe 4.0 x4 slots for secondary storage or games.

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