Minisforum has released the ESP4B PCIe expansion card, offering expanded storage connectivity through an ASMedia Promontory 21 chipset. The active cooled add in card supplies 4 M.2 slots, 4 SATA III ports, and a fast 20Gbps Type C connection. It is currently selling on retail platforms in China for 669 yuan, which converts to roughly $93 USD.
The ESP4B uses the Promontory 21 controller to distribute high speed lanes across multiple storage protocols. Upstream communication with the host motherboard relies on 4 PCIe Gen4 lanes. Downstream bandwidth splits into 8 PCIe Gen4 lanes, 4 PCIe Gen3 lanes, and dedicated USB routing. This setup allows users to expand their storage footprint without requiring motherboards with hardware level bifurcation support.
Minisforum assigns the 8 downstream PCIe Gen4 lanes directly to the M.2 slots. Builders can configure these slots as 2 full 4 lane drives or 4 individual 2 lane drives depending on their bandwidth requirements. The 4 PCIe Gen3 lanes route through an OCuLink 4i connector, which breaks out into 4 standard SATA III ports using a custom included cable. A single 20Gbps Type C port sits on the rear bracket for high speed external accessories. Active cooling keeps temperatures stable across all connected drives during heavy transfer workloads.
