It’s a weird fact of the modern PC industry, but the motherboard “chipset” or “Platform Controller Hub” (to use Intel’s terminology) is basically just a PCIe-attached I/O hub that exposes additional PCIe, USB, SATA, and platform services. Contemporary CPUs are built as SoCs, so all the essential functions to run the machine are integrated into the CPU itself. That’s why companies have started creating what are effectively I/O breakout boards by slapping motherboard chipsets onto PCI Express cards, including the one pictured above from WisdPi, as well as one coming from Minisforum, as spotted by PC Watch at Computex.
In the case of the AMD Promontory 21 chipset, it really is just a PCI Express I/O controller. In fact, AMD created the X670 chipset by simply wiring up two Promontory 21 chips in series. It’s the exact same chip, just used in pairs on the fancier motherboards, so you end up with piles of I/O, though it’s all running over the same PCI Express 4.0 x4 link to the CPU.
Two of the M.2 slots are on the front of the card, while a large black heatsink covers the Promontory 21 chip. (Image credit: WisdPi)
We’ve reported on cards like this before; this past December, we highlighted an open-source project for exactly this purpose, and of course, Asusd and ASRock have shipped expansion boards for specific motherboards that “upgrade” them from B650 to X670 by adding the second Promontory 21 chipset. All the way back in 2023, we also covered AMD engineers showing off the same thing in a Gamers Nexus video. Indeed, the very word “Promontory” refers to a projection from a larger body, such as a high cliff or, perhaps, an add-on card.
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So, the WisdPi “PROM21 All In Expansion Card” is a half-height PCI Express 4.0 add-in card that offers a whopping four M.2 slots, five USB 10 Gbps ports, six USB 2.0 ports, and an OCuLink port that supports PCI Express 4.0 or can breakout into four SATA ports. That’s more connectivity than some motherboards offer, which is no surprise, since the card costs $199 by itself, with no cables. WisdPi is primarily a Raspberry Pi shop, and as you’d expect, the card is compatible with Raspberry Pi devices that expose PCI Express, but that’s simply because it’s actually compatible with any PCI Express device, from AMD, Intel, Arm, or whoever.
The other two M.2 slots are on the back of the card, which could complicate cooling. (Image credit: WisdPi)
The card spotted by PC Watch at Minisforum’s Computex booth is similar in that it also offers four M.2 slots, an OCuLink connector, and at least one high-speed 20 Gbps USB port. However, it lacks the SATA functionality and the other USB ports of the WisdPi offering. Also, unlike WisdPi’s card, it seems that it will come with a dedicated cooling unit (with a blower fan and a shroud) for fast SSDs. That’s a little ironic considering the card seemingly limits drives to PCIe 4.0 x2 if you install all four, but “cooling” is better than “no cooling”. No word on how much the Minisforum offering will cost, but it will apparently be available in Q3 of this year.
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It’s almost a shame these cards aren’t more commonplace. For folks with machines based on entry-level motherboards, one of these cards could be just the ticket to expanding the I/O. Particularly on older-generation motherboards that usually had only one M.2 slot (if any), a card like one of these could enable significant storage expansion now that M.2 SSDs are the only type still being actively produced. You can check out PC Watch‘s photos of the Minisforum “PCIE TO 4” card at their post over here.
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