AMD B650 Expansion Card Unveiled: Add 4 M.2 Slots and 11 USB Ports via PCIe

Expansion products featuring AMD’s B650 chipset on PCI Express cards are making their way to the market. According to a report by Tom’s Hardware, two companies, WisdPi and Minisforum, have released or announced so-called “chipset expansion cards.” These products offer a highly practical solution for PC enthusiasts, allowing the addition of four M.2 NVMe slots and numerous USB ports with the use of just one PCIe slot.

The Technology Behind the Expansion Cards

At the heart of these products is AMD’s Promontory 21 chipset. It is widely known that modern CPUs (System-on-Chips, or SoCs) integrate essential functions such as memory controllers and PCIe lanes. As a result, the chipset essentially acts as a “PCIe-connected I/O hub,” providing additional PCIe lanes, USB ports, SATA ports, and more.

Promontory 21 exemplifies this concept. For instance, AMD achieves its high-end X670 chipset by linking two Promontory 21 chipsets in series. The essential difference between the B650 and X670 chipsets lies in whether one or two of these chips are used. Leveraging this characteristic, some niche products have already existed, providing I/O expansion on PCIe cards. WisdPi and Minisforum have now turned these into products aimed at the general market.

The WisdPi “PROM21” Overview

WisdPi’s “PROM21 All In Expansion Card” is a low-profile (half-height) PCI Express 4.0 add-in card, now available for purchase. According to the Tom’s Hardware article, its expandability surpasses that of many commercially available motherboards.

The specific interfaces include:

• M.2 Slots: 4 (PCIe 4.0-compatible; 2 mounted on the card’s surface, 2 on the back)
• USB 10Gbps Ports: 5
• USB 2.0 Ports: 6
• OCuLink Port: 1 (can be used as PCIe 4.0 or as 4 SATA ports)

The card features a total of 11 USB ports, plus the ability to connect external storage via OCuLink or legacy SATA devices. It is priced at $199, though cables need to be purchased separately. A large black heatsink on the card’s surface ensures cooling for the Promontory 21 chipset.

A notable feature is the cooling system for the two M.2 slots installed on the back of the card. Since SSDs are mounted on the backside, cooling could be a concern depending on the airflow within the PC case. Engineers should consider thermal solutions when utilizing the rear M.2 slots.

Features of the Minisforum Card

At Computex 2026, Minisforum showcased a similar expansion card concept at its booth, as revealed by PC Watch. Compared to WisdPi’s product, the Minisforum card has slightly different port configurations.

While the Minisforum card also includes four M.2 slots and an OCuLink connector, it lacks the five USB 10Gbps ports and six USB 2.0 ports present on WisdPi’s product. Instead, it features at least one high-speed USB 20Gbps port. It also appears to omit SATA functionality. Additionally, according to Tom’s Hardware, the card may include a dedicated cooling fan for operation.

Use Cases and Compatibility

These cards are designed for use not only with AMD platforms but also with Intel and Arm-based systems. According to WisdPi, the product is compatible with any device that has a PCIe interface. It is particularly targeted at users who want to expand PCIe slots on single-board computers (SBCs) like the Raspberry Pi. WisdPi is primarily a manufacturer of accessories for Raspberry Pi, and the company has explicitly aimed this product at SBC users.

Potential use cases include:

• Enhancing I/O on Mini PCs: Especially for Mini PCs without Thunderbolt or USB4 support but with available PCIe slots, this card can significantly expand NVMe storage and USB ports.
• Turning SBCs into Fully-Featured Storage Devices: Connecting to PCIe-enabled SBCs like the Raspberry Pi CM4 to build a NAS or server with multiple high-speed NVMe storage options.
• Restoring I/O on Faulty Motherboards: If the chipset functions on a motherboard are damaged, but the CPU-connected PCIe slot is still operational, this card could potentially restore I/O functionalities.

Performance Considerations

The Promontory 21 connects to the CPU via a PCI Express 4.0 x4 link, meaning that all devices connected to the expansion card share a maximum bandwidth of approximately 8GB/s (the theoretical limit of PCIe 4.0 x4).

It would be challenging to achieve the peak performance of all four M.2 NVMe SSDs simultaneously. If all slots were populated with high-speed Gen4 SSDs, running simultaneous benchmarks would likely result in a bandwidth bottleneck. However, in practical scenarios such as storage servers or everyday use, it’s rare for all SSDs to demand full bandwidth at the same time, so this limitation is unlikely to cause significant issues. USB and SATA ports also share this bandwidth, which should be taken into account during system design.

Comparison with Existing Products

This type of card is not entirely new. In the past, companies like ASUS and ASRock offered expansion cards aimed at upgrading specific motherboards from B650 to X670 functionality. Additionally, open-source projects with similar goals have also existed.

The products from WisdPi and Minisforum, however, stand out because they are not tied to specific motherboards and can operate in any generic PCIe slot. This makes them a more attractive option for a wider range of users. At $199, the WisdPi card is competitively priced compared to buying separate M.2 expansion cards and USB hubs.

Editorial Perspective

Short-Term Impact: These expansion cards are a powerful upgrade option for systems with available PCIe slots but limited I/O ports, particularly Mini PCs and workstations. Over the next 3–6 months, we expect to see more similar products on platforms like Amazon and AliExpress, potentially sparking price competition. WisdPi’s $199 pricing will likely pressure competitors to price their products competitively. Engineers should evaluate products in this category as a solution to meet system I/O requirements.

Long-Term Outlook: The trend of repurposing chipsets as general-purpose I/O controllers in PCIe card form is an example of the ongoing “fluidization” of PC architecture. With clear distinctions between CPU and chipset roles, users are gaining the ability to customize their I/O capabilities as needed. Over the next 1–3 years, standardized modular I/O systems might influence the design philosophy of DIY PCs and industrial PCs. As USB4 and Thunderbolt adoption grows, the demand for these PCIe cards could change, which warrants close monitoring.

Editorial Questions: When considering these products, how should we evaluate the actual usage frequency of M.2 slots and USB ports against the bandwidth limitations of PCIe 4.0 x4? Additionally, for SBC users, an unresolved question is whether these cards can operate stably in power-constrained environments like Raspberry Pi. What challenges do our readers anticipate in real-world scenarios?

Reference

• AMD B650 expansion cards hit retail starting at $199 — add four M.2 PCIe 4.0 slots and 11 USB ports to any PC with a PCIe slot - Tom’s Hardware — Published June 6, 2026