Minisforum ESP4B Expansion Card Adds AMD B850 Chipset, Four M.2 Slots, OCuLink, and 20Gbps USB-C
Minisforum has introduced a new PCIe expansion card that could be a practical upgrade for PC builders who need more high-speed storage without relying on motherboard PCIe bifurcation. The new card, called the Minisforum ESP4B, is built around AMD’s B850 chipset and brings four M.2 SSD slots to a system through a single PCIe 4.0 x4 connection.
What makes the ESP4B especially interesting is that it does not require PCIe bifurcation support from the motherboard. That matters because many consumer systems, older desktops, and compact PCs either lack bifurcation entirely or offer limited configuration options in BIOS. With the chipset integrated directly onto the add-in card, the ESP4B handles the lane distribution itself.
According to Minisforum, the card uses AMD’s Promontory 21 chipset variant and connects to the host machine through PCIe 4.0 x4. From there, it can support up to four M.2 SSDs, although the available bandwidth changes depending on how many drives are installed.
A user who tested the card shared early hands-on results, giving a clearer look at real-world behavior. When one or two M.2 drives are installed, the first two SSDs can operate at PCIe 4.0 x4 speeds. In testing, a Kingston PCIe Gen 4 SSD reached around 6.1 GB/s in read performance, which is close to what users would expect from a native PCIe 4.0 connection.
When all four M.2 slots are populated, the card automatically shifts the drives to PCIe 4.0 x2 mode. In that setup, read speeds were reported at around 3.3 GB/s per drive. While this is lower than full x4 performance, it is still fast enough for many demanding workloads, including large file transfers, media libraries, game storage, and productivity tasks.
Compatibility appears to be another strong point. The expansion card was reportedly tested on several platforms, including much older hardware such as a 2011 Dell OptiPlex 900. It was also shown working with an ARM-based Minisforum system, suggesting that the ESP4B may be useful beyond standard Intel and AMD desktop builds.
In addition to the four M.2 slots, the Minisforum ESP4B includes an OCuLink port. This gives users the option to connect an external GPU, which could be useful for compact PCs, mini PCs, or systems where internal graphics expansion is limited. The same interface can also be switched to support four SATA devices through the included adapter, adding even more flexibility for storage-focused builds.
The card also includes a 20Gbps USB Type-C port, giving users another high-speed connection for external drives, docks, capture devices, or other bandwidth-heavy peripherals.
B850-based add-in cards are still uncommon, making the ESP4B one of the more notable options in this category. Similar expansion cards based on AMD’s B650 chipset have appeared recently, but Minisforum’s B850 model stands out for its combination of four M.2 slots, OCuLink support, SATA expandability, and fast USB-C connectivity.
The main drawback is price. At around $135, the Minisforum ESP4B is not exactly cheap, especially compared with simpler M.2 expansion cards. However, the onboard chipset, broad compatibility, and lack of bifurcation requirements could make it worth considering for users who need multiple NVMe SSDs in systems that would otherwise struggle to support them.
For PC enthusiasts, homelab users, compact workstation builders, and anyone trying to expand storage on older or limited motherboards, the Minisforum ESP4B could be a surprisingly flexible solution. It combines modern PCIe 4.0 storage expansion with extra connectivity options, making it more than just a basic M.2 adapter.
