ASUS PRIME B850M-K Motherboard AMD Socket AM5 DDR5
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ASUS PRIME B850M-K — AM5 micro-ATX with a PCIe 5.0 graphics slot, Gen5 M.2 and 2.5Gb LAN
An AMD B850 micro-ATX board for Ryzen 9000, 8000 and 7000 Series processors up to 170 W. ASUS gives it an 8+2+1 phase Digi+ power design, a PCIe 5.0 x16 SafeSlot for the graphics card, an M.2 slot at PCIe 5.0 x4 under a heatsink plus a second at PCIe 4.0 x4, two DDR5 slots up to 128 GB, and Realtek 2.5Gb Ethernet. There is no Wi-Fi on this model.
Board Map
What sits where on the PRIME B850M-K
AMD Socket AM5 — Centre
Takes AMD Ryzen 9000, 8000 and 7000 Series desktop processors up to 170 W. With Ryzen 9000, the BIOS adds ASUS AI Cache Boost, which tunes cache and memory paths for local AI workloads.
8+2+1 phase power under the VRM heatsink — Top & Left
Digi+ VRM with discrete MOSFETs, a single heatsink with a thermal pad over the MOSFETs and chokes, fed by one 8-pin CPU connector.
2 × DDR5 DIMM slots — Right
Dual-channel DDR5 up to 128 GB, ECC and non-ECC un-buffered DIMMs, AMD EXPO and ASUS Enhanced Memory Profile (AEMP) for kits without EXPO.
M.2_1 under the heatsink — Below the socket
PCIe 5.0 x4 (2280) with Ryzen 9000 and 7000, covered by the M.2 heatsink. M.2_2 below runs at PCIe 4.0 x4 (2242/2260/2280).
PCIe 5.0 x16 SafeSlot — Mid board
The top x16 slot is wired to the CPU at PCIe 5.0 x16 with Ryzen 9000/7000 (PCIe 4.0 x8 or x4 with Ryzen 8000), in a reinforced metal SafeSlot. The second x16-size slot runs at PCIe 4.0 x4 from the chipset.
Chipset, SATA and headers — Lower right
B850 under an aluminium passive heatsink, 4 × SATA 6Gb/s, a front USB-C 5Gbps connector, 3 ARGB Gen 2 headers, a COM header, an SPI TPM header and the Q-LED Core indicator.
Power Delivery & Cooling
What feeds the socket, and what keeps it cool
8+2+1 Phase, Discrete MOSFETs
ASUS uses discrete MOSFETs for efficient, stable power to Ryzen processors, with a Digi+ VRM that controls voltage droop and switching frequency in real time.
VRM Heatsink & Thermal Pad
One large VRM heatsink sits on a thermal pad over the MOSFETs and chokes, shown here on the angled board.
M.2 & Chipset Heatsinks
The M.2 heatsink keeps the Gen5 SSD from throttling during long transfers, and the B850 chipset is cooled by a passive aluminium heatsink with no fan to clog with dust.
Hybrid Fan Headers
One CPU fan and three chassis fan headers each detect PWM or DC fans, can follow three temperature sources, and have their own over-current protection. Fan Xpert 2+ sets the curves.
Lane Map
Interface speed rating & capability relative to modern motherboard standardsRear I/O Bay
Exactly what appears on the back of your case — stainless-steel back I/O, separate I/O shield in the box
Will It Fit Your Build?
Check these before you add to cartTwo memory slots
There are 2 DDR5 slots (up to 128 GB). Buy a two-stick kit of the total you want now, because there are no spare slots for adding more later.
No Wi-Fi or Bluetooth
Networking is 2.5Gb Ethernet only. For wireless, add a PCIe or USB Wi-Fi adapter.
Processor
AMD Ryzen 9000, 8000 and 7000 Series on AM5, up to 170 W. Ryzen 8000 chips run the top x16 slot at PCIe 4.0 (x8 or x4) and M.2_1 at PCIe 4.0 x4.
Power supply
One 8-pin CPU (EPS) connector and the 24-pin ATX cable.
Case
micro-ATX, 24.4 × 22.1 cm. Fits micro-ATX and ATX cases, with front headers for USB-C 5Gbps, USB 5Gbps and USB 2.0.
Graphics & storage
A PCIe 5.0 x16 graphics slot and a PCIe 5.0 x4 M.2 slot with Ryzen 9000/7000, plus a second M.2 and 4 SATA ports.
Full Specification Sheet
ASUS PRIME B850M-K| CPU Socket | AMD Socket AM5 |
| CPU Support | AMD Ryzen 9000 / 8000 / 7000 Series desktop processors, up to 170 W |
| Chipset | AMD B850 |
| Form Factor | micro-ATX, 24.4 × 22.1 cm (9.6 × 8.7 in) |
| Power Design | 8+2+1 phase Digi+ VRM, discrete MOSFETs, 1 × 8-pin CPU power |
| Memory | 2 × DDR5 DIMM, dual channel, up to 128 GB, ECC and non-ECC un-buffered |
| Memory Speed (OC) | 8200+ MT/s with Ryzen 9000, 9600+ MT/s with Ryzen 8000, 8000+ MT/s with Ryzen 7000; AMD EXPO, ASUS AEMP |
| Expansion Slots | 1 × PCIe 5.0 x16 (CPU; PCIe 4.0 x8/x4 with Ryzen 8000), 1 × PCIe 4.0 x16 slot at x4 (chipset) |
| M.2 Storage | M.2_1 PCIe 5.0 x4 (2280), M.2_2 PCIe 4.0 x4 (2242/2260/2280); Ryzen 8000: both PCIe 4.0 |
| SATA & RAID | 4 × SATA 6Gb/s; AMD RAIDXpert2 (RAID 0/1/5/10 with Ryzen 9000) |
| LAN | Realtek 2.5Gb Ethernet, ASUS LANGuard |
| Wireless | None |
| Audio | Realtek 7.1 surround HD audio codec, up to 24-bit / 192 kHz, audio shielding |
| Rear USB | 2 × USB 10Gbps Type-A, 2 × USB 5Gbps Type-A, 4 × USB 2.0 Type-A |
| Front USB Headers | 1 × USB 5Gbps Type-C connector, 1 × USB 5Gbps header (2 ports), 2 × USB 2.0 headers (4 ports) |
| Video Outputs | HDMI (4K 60Hz, HDMI 2.1), DisplayPort (8K 30Hz, DP 1.4) |
| Internal Headers | 1 × CPU fan, 3 × chassis fan, 3 × ARGB Gen 2, COM, S/PDIF out, SPI TPM, front audio, Clear CMOS |
| BIOS | 256 Mb flash ROM, UEFI AMI BIOS; BIOS FlashBack button and LED, Q-LED Core |
| OS Support | Windows 11, Windows 10 64-bit |
