ASUS PRIME B840M-K — AMD B840 Micro ATX for Socket AM5 with DDR5 and Dual M.2
AMD B840 / Socket AM52 x M.2 PCIe 4.0Realtek 2.5Gb EthernetSupports CPUs up to 170 W
The ASUS PRIME B840M-K is a micro ATX motherboard on the AMD B840 chipset for Socket AM5, built as a clean, no-frills base for Ryzen desktop builds that need solid storage and networking rather than overclocking headroom. It carries the part number 90MB1PK0-M0EAY0 (EAN 4711636435048) and supports AMD Ryzen 9000, 8000 and 7000 Series processors up to 170 W TDP, with two DDR5 slots for up to 128 GB. Storage runs to two PCIe 4.0 x4 M.2 slots and four SATA 6 Gb/s ports, networking to a Realtek 2.5Gb Ethernet port with LANGuard surge protection, and audio to a Realtek 7.1 codec with a shielded layout. Typically in stock with fast delivery across Cyprus.
Compatibility — check before buying:
The B840 chipset is AMD’s entry tier for AM5: it supports memory overclocking through EXPO and ASUS AEMP, but CPU overclocking is not part of the B840 feature set. If you plan to push a Ryzen 9 with a manual all-core overclock, choose a B850 or X870 board instead. The graphics slot is PCIe 4.0, not PCIe 5.0, and it runs at x16 with Ryzen 9000 and 7000 Series but drops to x8 or x4 with Ryzen 8000 Series chips. There are only 2 DDR5 slots, so 128 GB means two 64 GB modules; DDR4 does not fit AM5. Display output is a single HDMI port and needs a CPU with integrated graphics — there is no DisplayPort and no second output for dual monitors from the iGPU. The board has no Wi-Fi and no Bluetooth. It measures 24.4 x 22.1 cm (micro ATX), and there is no rear USB Type-C port — the 5 Gbps Type-C is a front-panel header.
Best For
✓ Value AM5 builds pairing a Ryzen CPU with a discrete graphics card
✓ Office and business desktops on wired 2.5Gb networking
✓ Systems with two NVMe drives plus SATA hard disks
✓ Upgrades from AM4 that move to DDR5 without paying for PCIe 5.0
✓ Builds where a front USB-C port matters more than a rear one
✓ Compact micro ATX cases at 24.4 x 22.1 cm
Key Features
Socket AM5 with support for CPUs up to 170 W
The board covers AMD Ryzen 9000, 8000 and 7000 Series processors with a 170 W TDP ceiling, which includes the top Ryzen 9 parts. AI Cache Boost and the ASUS BIOS tuning options are available, and DDR5 memory reaches a rated 8000+ MT/s when overclocked via EXPO or the ASUS AEMP profiles.
Two PCIe 4.0 x4 M.2 slots plus four SATA ports
Both M.2 slots take 2280 drives and run at PCIe 4.0 x4 with Ryzen 9000 and 7000 Series processors, with M.2_2 falling back to x4 or x2 on Ryzen 8000. Four SATA 6 Gb/s connectors remain for hard disks and 2.5-inch SSDs, so a boot NVMe, a games NVMe and bulk storage all fit.
Realtek 2.5Gb Ethernet with LANGuard
A Realtek 2.5Gb Ethernet controller gives two and a half times gigabit throughput on the local network, with ASUS LANGuard surge and static protection on the port. There is no wireless module on this model, so plan on a cable run or a separate Wi-Fi adapter.
Realtek 7.1 audio with shielding, and Aura Sync
The onboard Realtek 7.1 surround High Definition Audio codec supports 24-bit / 192 kHz playback, with audio shielding and dedicated PCB layers separating the analogue section from digital noise. Aura Sync headers let the board drive addressable lighting in step with the rest of the build.
Technical Specifications
| Identification |
| Brand |
ASUS |
| Series |
PRIME |
| Model |
PRIME B840M-K |
| Part Number / MPN |
90MB1PK0-M0EAY0 |
| EAN / GTIN |
4711636435048 |
| Platform |
| Chipset |
AMD B840 |
| CPU Socket |
AMD Socket AM5 |
| CPU Support |
AMD Ryzen 9000, Ryzen 8000 and Ryzen 7000 Series, up to 170 W TDP |
| CPU Overclocking |
Not supported on the B840 chipset |
| Form Factor |
Micro ATX — 24.4 x 22.1 cm (9.6 x 8.7 in) |
| Memory |
| Slots |
2 x DDR5 DIMM, dual channel |
| Maximum Capacity |
128 GB (64 GB per DIMM) |
| Rated Speeds |
Up to DDR5-8000+ (OC) |
| Profiles |
AMD EXPO and ASUS AEMP |
| Expansion and Graphics |
| PCIe x16 (CPU) |
1 x PCIe 4.0 x16 — x16 on Ryzen 9000 / 7000, x8 or x4 on Ryzen 8000 |
| PCIe x16 (Chipset) |
1 x PCIe 3.0 x16 slot running at x4 |
| Display Output |
1 x HDMI, 4K at 60 Hz per HDMI 2.1 |
| Graphics Note |
HDMI output requires a CPU with integrated graphics |
| Storage |
| M.2 Slot 1 (M.2_1) |
PCIe 4.0 x4, type 2280 |
| M.2 Slot 2 (M.2_2) |
PCIe 4.0 x4, type 2280 — x4/x2 on Ryzen 8000 Series |
| SATA |
4 x SATA 6 Gb/s |
| Connectivity |
| LAN |
Realtek 2.5Gb Ethernet with ASUS LANGuard |
| Wireless |
None — no Wi-Fi or Bluetooth module |
| Rear USB |
4 x USB 5Gbps Type-A, 2 x USB 2.0 Type-A |
| Internal USB |
1 x USB 5Gbps Type-C connector, 1 x USB 5Gbps header, 2 x USB 2.0 headers |
| Audio |
Realtek 7.1 Surround High Definition Audio CODEC, 24-bit / 192 kHz, with audio shielding |
| Board Features |
| Lighting |
Aura Sync addressable headers |
| Memory Tuning |
AMD EXPO and ASUS AEMP II profiles |
| Performance |
AI Cache Boost |
| In the Box |
| Contents |
2 x SATA cables, I/O shield, M.2 screw package, quick start guide |
| Warranty |
| Warranty |
1-Year Warranty (Singular) |
Frequently Asked Questions
Can I overclock the CPU on the ASUS PRIME B840M-K?
No. AMD’s B840 chipset does not include CPU overclocking — that is the main line separating it from B850 and X870. What you do get is memory overclocking through AMD EXPO and the ASUS AEMP profiles, with DDR5 rated to 8000+ MT/s. Precision Boost still works normally, so a Ryzen 9 will reach its stock boost clocks on this board.
Does this board support PCIe 5.0 or Wi-Fi?
Neither. The graphics slot is PCIe 4.0 x16 with Ryzen 9000 and 7000 Series CPUs, and both M.2 slots are PCIe 4.0 x4. There is no wireless module either, so networking is the Realtek 2.5Gb Ethernet port or a separate PCIe or USB Wi-Fi adapter. If you want Wi-Fi on the board, look at the PRIME B840M-A WIFI instead.
Can I run two monitors from the integrated graphics?
Not from the board’s own outputs — there is a single HDMI port and no DisplayPort. With a CPU that has integrated graphics you get one 4K 60 Hz display over HDMI. For multiple monitors you will need a discrete graphics card in the PCIe 4.0 x16 slot.
What do I need to know before buying this board?
It is micro ATX at 24.4 x 22.1 cm. There are two DDR5 slots, so buy a matched 2-module kit — DDR4 is not compatible with AM5. The USB Type-C port is a front-panel header, not a rear port. The box includes two SATA cables, the I/O shield, M.2 screws and a quick start guide, but no Wi-Fi antenna since there is no wireless module.
Singular Expert Insight
The B840M-K is the sensible floor of the AM5 range rather than a compromise: you lose CPU overclocking and PCIe 5.0, but you keep the socket, DDR5, two Gen 4 M.2 slots and 2.5Gb Ethernet — the things most people actually use. If your build is a Ryzen 7 with a graphics card and two NVMe drives, this board does the job for noticeably less than a B850. Just be honest about the two DIMM slots and buy the
DDR5 memory as one matched kit from the start, because adding a second pair later is not an option. The other thing to plan for is the single HDMI output: fine for a build with a discrete card from our
graphics cards range, awkward if you were counting on driving two monitors from the CPU integrated graphics. If either the overclocking or the second display output matters, spend the extra on a B850 board.
Buyer's Guide
Buy it if
You want a straightforward, well-built AM5 base for a Ryzen 9000 or 7000 build with two Gen 4 M.2 drives, 2.5Gb wired networking and a discrete graphics card, at the lowest sensible price.
Skip it if
You want to overclock the CPU, you need PCIe 5.0 for graphics or storage, you need Wi-Fi, or you plan to drive more than one monitor from the processor integrated graphics.
Also consider
The ASUS PRIME B840M-A WIFI if you need wireless and a second display output, or the GIGABYTE B850M FORCE if PCIe 5.0 and three M.2 slots are worth the difference.