B840 is the entry-level chipset in AMD's 800-series for AM5. It arrived in early 2025 alongside B850. The name suggests a slightly trimmed B850, but it is closer to A620: there is no CPU overclocking, no PCIe 5.0, and the chipset's own lanes are PCIe 3.0. It is a reasonable base for a plain Ryzen build if the price is right. The boards we track are on the B840 deals page.
Cheapest B840 boards right now
All 16 B840 motherboards, with price drops and price history
Amazon Warehouse offers on B840 boards
Where B840 sits
From the top, the 800-series for AM5 is X870E, X870, B850 and B840. In AMD's naming, B has usually meant a mainstream chipset that overclocks, and A has meant the basic tier that does not. B840 breaks that pattern. It carries a B name but has the restrictions of an A-series part, and in practice it sits beside A620 from 2023 rather than above it by any great distance. If the letters are new to you, motherboard chipsets explained covers what each tier means.
Key specifications
| Feature | B850 | B840 | A620 |
|---|---|---|---|
| Launched | Early 2025 | Early 2025 | 2023 |
| CPU overclocking | Yes | No | No |
| Memory overclocking (EXPO / XMP) | Yes | Yes | Yes |
| PCIe 5.0 M.2 slot | Required | No | No |
| PCIe 5.0 graphics slot | Optional, varies by board | No | No |
| Graphics slot and main M.2 | PCIe 5.0 or 4.0 | PCIe 4.0 | PCIe 4.0 |
| Chipset lanes | PCIe 4.0 | PCIe 3.0 | PCIe 3.0 |
The graphics slot and the main M.2 slot are wired to the processor and run at PCIe 4.0. Anything connected through the chipset, such as a second M.2 slot on some boards, runs at PCIe 3.0 at most.
What that means in use
For a typical PC, less than the table suggests. A graphics card in a PCIe 4.0 x16 slot is not held back in any way you would notice, and a PCIe 4.0 SSD in the main slot is as fast as most people will ever use. The PCIe 3.0 chipset lanes matter if you add a second fast NVMe drive: it will work, but at roughly half the peak transfer speed the drive could manage in a PCIe 4.0 slot. For a games library or general storage that is rarely a problem you will feel.
No CPU overclocking means you cannot raise the multiplier on a Ryzen chip. Ryzen processors already boost themselves close to their limits, so the loss is small for most people. Memory overclocking remains, so you can load an EXPO or XMP profile and run DDR5 at its rated speed.
Compatible CPUs and memory
B840 boards support the AM5 desktop range: Ryzen 7000, Ryzen 8000G and Ryzen 9000, with DDR5 memory only. The socket is the same as on the most expensive boards, so the upgrade path is the same too. AMD has said AM5 is supported through 2027 and beyond.
Supporting a chip and running it well are different things. Entry-level boards usually have simpler power delivery and smaller heatsinks. That is fine for a Ryzen 5 or a 65 W Ryzen 7. If you intend to fit a 12- or 16-core processor, check the board's CPU support list and consider B850 instead. VRMs explained covers when this matters.
What varies by board
- Memory slots. Some entry-level boards have two slots and some have four. Two is enough for most builds, but it limits adding memory later.
- M.2 slots. How many there are, and whether the second one runs from the processor at PCIe 4.0 or from the chipset at PCIe 3.0.
- Rear ports. USB port count and speeds differ a good deal at this level.
- WiFi. Often sold as a separate, slightly dearer version of the same board.
- Size. Many B840 boards are micro-ATX, which fits both small and full-size cases; check the form factor on the listing.
Who should buy B840
B840 suits an office PC, a family computer, or a modest gaming build with a Ryzen 5 and a mid-range graphics card, where you will fit the parts once and leave them alone. It also suits a build around a Ryzen 8000G chip using integrated graphics, since those processors are PCIe 4.0 parts and cannot use PCIe 5.0 slots anyway.
It is the wrong choice if you want to tune the CPU, plan to add several NVMe drives, or expect to move to a high-end processor later. In those cases B850 is the better starting point, and a discounted B650 board is worth a look as well. How much to spend on a motherboard sets out where the extra money goes.
What to check on the listing
- That it really is B840 and not B850. Model names from the same maker can differ by one digit.
- The number of memory slots and M.2 slots.
- Video outputs on the rear panel, if you are relying on integrated graphics.
- WIFI or non-WIFI version.
- Compare it with A620 and B650 boards at a similar price before deciding, because the three overlap.
Current prices and any reductions are on the B840 deals list. Opened and returned boards appear on the Warehouse page.
Questions people ask
Can you overclock on a B840 motherboard?
Not the CPU. B840 does not allow CPU overclocking. Memory overclocking is allowed, so EXPO and XMP profiles work.
Does B840 support PCIe 5.0?
No. On B840 the graphics slot and the main M.2 slot run at PCIe 4.0, and the lanes provided by the chipset are PCIe 3.0. For a guaranteed PCIe 5.0 M.2 slot you need B850 or above.
Is B840 better than A620?
They are close. Both lack CPU overclocking and PCIe 5.0, and both have PCIe 3.0 chipset lanes. B840 boards are newer designs. Choose between them on the features and price of the individual boards.
Will a B840 board run a Ryzen 9000 processor?
Yes. B840 uses the AM5 socket and supports Ryzen 7000, 8000G and 9000 processors. For the highest-power chips, check the CPU support list of the specific board, because entry-level boards have simpler power delivery.