PRIME B840M-A (-CSM)
The ASUS PRIME B840M-A (-CSM) is a Micro ATX AM5 motherboard on the B840 chipset. It supports DDR5 memory up to 7,600 MT/s and 3 M.2 slots. Full specs, power delivery, and current prices are below.
Prices update regularly and may differ at the retailer. This page contains affiliate links.
MaxMyBuild scores
How we score →How well the PRIME B840M-A (-CSM) is equipped for gaming and for productivity, scored 0–100 from its specs. Scores are fit-for-purpose: a capable board can top the gaming score without being the most expensive.
Weighs CPU power delivery, memory speed support, the GPU PCIe slot, Wi-Fi version, and M.2 storage — the things that actually matter for a gaming build.
Rewards fast, plentiful M.2 storage and USB I/O, PCIe expansion, memory capacity and slots — what matters for content creation and heavy multitasking.
CPU power
224 W
Limited · 0.9x
Wired for about 224 W, roughly 97% of the 230 W that the top Ryzen 9 chips pull. Pair it with a mid-range processor rather than a flagship. The figure comes from its 2x4+2+1 power-stage (VRM) layout and 8 EPS connectors. It is a rating of what the board is built to deliver, not a measurement, so treat it as headroom rather than a guarantee.
Specifications
Platform
- Chipset
- B840
- Socket
- AM5
- Form factor
- Micro ATX
Memory
- Type
- DDR5
- Slots
- 4
- Max speed
- 7,600 MT/s
- Max capacity
- 256 GB
- Channels
- 2-channel
- ECC / memory
- UDIMM
Power & VRM
- CPU power
- 224 W
- Phase config
- 2x4+2+1
- VRM stages
- 1H/1L
- EPS power
- 8
- VRM heatsink
- Full coverage
Storage & Expansion
- M.2 slots
- 3
- M.2 layout
- 2× PCIe 4.0 ×4, 1× PCIe 3.0 ×4
- M.2 heatsinks
- Slots 1
- SATA ports
- 4 SATA3
- PCIe ×16 slots
- 1× PCIe 4.0 ×16, 2× PCIe 3.0 ×1
Ethernet & Wi-Fi
- Realtek RTL8125
- 2.5 GbE
- Ethernet ports
- 1
- Wi-Fi
- None
USB & I/O
- Rear USB-A
- 4× USB 2.0, 2× 10 Gbps
- Rear USB-C
- 1× 5 Gbps
- Front USB-C
- 1× 5Gbps
- Front USB 3 headers
- 1
- Front USB 2 headers
- 2
Audio & Video
- Audio codec
- ALC897
- Audio jacks
- 3
- HDMI
- HDMI 2.1
- DisplayPort
- 2× DP 1.4
- USB-C video
- None
Cooling, RGB & Design
- Fan headers
- 4
- 5V ARGB headers
- 3
- PCB colour
- Black, White
- Heatsink colour
- Silver, Grey
Onboard & Diagnostics
- BIOS Flashback
- Yes (rear)
- Diagnostics
- Power/status LEDs
- TPM header
- Yes
Compare the PRIME B840M-A (-CSM) against every other board on the motherboard comparison table. Not sure it fits your chip? The socket compatibility guide explains AM5 pairings.
Where to buy the PRIME B840M-A (-CSM)
Every in-stock retailer offer we track, cheapest first.
| Retailer | Availability | Price | Buy |
|---|---|---|---|
| Amazon | In stock | $240.99 |  |
The PRIME B840M-A (-CSM) starts from $240.99 across 1 retailer (No onboard Wi-Fi). Prices update daily from live stock.
Which CPUs fit the PRIME B840M-A (-CSM)?
Compare all CPUs →In-stock AM5 processors this board can run, socket-matched and within its 224 W power budget, ranked by gaming value (performance per dollar).
| Processor | Cores | Gaming | From | |
|---|---|---|---|---|
 | Ryzen 5 9600X AMD | 6/12 | 72.6 | $173.00 |
 | Ryzen 5 7600X AMD | 6/12 | 67.3 | $163.00 |
 | Ryzen 5 8500G AMD | 6/12 | 52.0 | $146.99 |
 | Ryzen 5 8400F AMD | 6/12 | 50.0 | $149.00 |
 | Ryzen 5 7500F AMD | 6/12 | 61.0 | $189.99 |
 | Ryzen 5 7600 AMD | 6/12 | 63.4 | $209.00 |
 | Ryzen 7 7700X AMD | 8/16 | 70.6 | $233.00 |
 | Ryzen 5 8600G AMD | 6/12 | 55.0 | $186.30 |
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