Minisforum ESP4B Puts Four NVMe Drives, OCuLink and USB-C on One Card

The Minisforum ESP4B is a PCIe card for people whose mini PC ran out of room. It takes one PCIe 4.0 x4 slot and turns it into four M.2 NVMe slots, an OCuLink port that runs four SATA drives, and a 20Gbps USB-C port, all through an AMD desktop chipset that does the splitting so your motherboard doesn’t have to. Minisforum lists it at $135.90 on sale from $169, with shipping expected in late October. None of those pieces are new. The price is what caught my eye, and I’ll explain why.

I’ve been doing home labs for a long time. I’ve been in the industry for over 20 years, and on the professional side I’m a principal security engineer. My labs have gone from enterprise-grade hardware, to regular consumer hardware, to mini PCs. That’s because for the first time, in just the last few years, mini PCs have the power and the capacity to actually run all these environments and handle the heavy workloads. Their only real limit is their size. Because they’re so small, they trade away expandability. So you’re always on the lookout for the most expandable mini PC in the smallest box, and that’s where cards like this come in. None of the pieces are new on their own. We’ve had NVMe expansion cards, OCuLink cards and USB-C cards. WisdPi even put them all on one card back in June. But Minisforum is doing it for $135.90, with the SATA cable in the box, and that price is what gets me excited.

What is the Minisforum ESP4B?

It’s a PCIe expansion card that uses an AMD desktop chipset as a traffic cop. The chip on the board is AMD’s Promontory 21, the same silicon that sits on B650 and B850 motherboards, and Minisforum’s own render of the underside says it plainly: “PROM21 TO 4NVME”. Minisforum’s spec sheet lists the chip as “AMD B650/B850”, and an owner’s teardown reported by VideoCardz found the newer B850-era revision on that unit. Since Minisforum lists both, you could get either.

What that chip gives you is four M.2 2280 slots, one OCuLink port and one USB-C port, hanging off a single PCIe 4.0 x4 connection to your PC. Minisforum says it works on Intel and AMD platforms. The card first showed up as a prototype at Computex in June, and the store listing went live on September 28.

Does it need PCIe bifurcation?

No, and that’s the whole point of putting a chipset on the card. Cheaper four-drive cards like Sabrent’s $99.99 EC-P4BF are passive: they only work if your motherboard can split one x16 slot into four x4 links, a BIOS feature called bifurcation that a lot of mini PCs and older desktops don’t have. The ESP4B’s Promontory 21 does that splitting itself, so any PCIe 4.0 x4 or wider slot will do.

You’ve been able to buy switch-based cards before, but they haven’t been cheap. Sabrent’s switch card, the EC-P3X4, is $179.99 and runs at PCIe 3.0. HighPoint’s Gen4 Rocket 1504 is $639. Against those, $135.90 for a Gen4 switch card is the news here.

How fast are the drives with all four installed?

Slower than two, because they all share one pipe. The host link is PCIe 4.0 x4, which Minisforum rates at up to 8 GB/s. With drives only in slots 1 and 2, each one gets a full PCIe 4.0 x4 link. Fill all four slots and every drive drops to PCIe 4.0 x2.

One owner’s measurements, reported by VideoCardz, line up with that. A Gen4 SSD read at 6.13 GB/s in an x4 slot on the card, close to the 6.08 GB/s the same drive managed in the motherboard’s own M.2 slot, and 3.29 GB/s in an x2 slot. A Gen3 drive did 2.92 GB/s and 1.62 GB/s in the same two positions. So two fast drives lose almost nothing, and four fast drives run at roughly half speed each, with the USB-C port and OCuLink sharing that same uplink whenever they’re busy.

What does the OCuLink port do?

Out of the box, it runs four SATA drives. The included cable breaks the OCuLink port out into four SATA 3.0 data connectors, so you can hang four hard drives off the card. Power for those drives isn’t included, so you’ll need SATA power from your PC’s supply or an external source.

Flip a physical switch on the board, marked “PCIE SATA” next to the bracket, and the port becomes a PCIe 3.0 OCuLink port instead. Minisforum’s pages say only “switchable to PCIe 3.0 mode”. Going by AMD’s chipset table, which lists the B850’s four SATA ports as “or PCIe 3.0”, that’s likely a PCIe 3.0 x4 link, though Minisforum doesn’t state the lane count.

Can it run an eGPU? Minisforum doesn’t claim it anywhere. The same owner’s review reported by VideoCardz says they tested PCIe mode with Minisforum’s DEG2 eGPU dock, but that’s one person’s report, and a PCIe 3.0 x4 link is well short of what a modern graphics card wants. Treat eGPU use as a maybe, outside what Minisforum promises.

Will it fit a Minisforum MS-01?

Minisforum hasn’t said. There’s no compatible-systems list on any of its store pages. Here’s what the facts say. The card is low-profile, 69 mm tall and 168 mm long, it ships with the low-profile bracket fitted and a full-height bracket in the box, and it has a blower fan under a shroud, so it’s thicker than a bare board. Minisforum doesn’t publish the thickness.

The MS-01 has a half-height, single-slot PCIe 4.0 x16 slot that runs at x8, so the height and the electrical side match. Whether the fan shroud clears the MS-01’s single-slot opening is the open question, and only Minisforum or an owner can answer it. The MS-03’s slot takes cards up to 170 mm long and 20 mm thick, so the ESP4B’s length fits there, and the MS-S1 MAX’s slot is PCIe 4.0 x4, which matches the card exactly. If you have an MS-02 Ultra, you already have bifurcation on one of its slots, so a passive card is an alternative.

ESP4B vs WisdPi PROM21 All in: which is the better deal?

It comes down to USB ports versus price, cooling and a store you’ve heard of. WisdPi’s PROM21 All in is the same idea on the same chip: four M.2 slots, an OCuLink port that switches between PCIe and SATA, and a 20Gbps USB-C port. On top of that it has four 10Gbps USB-A ports, six internal USB 2.0 headers and an external power connector, and it works on x86 and Arm systems. It launched at $199 in June and sells for $149 now, with the SATA cable another $15.

The ESP4B skips the extra USB ports and gives you an active cooler, US, UK and EU stores, and the SATA cable in the box, for $135.90. With cables, that’s about $28 less than WisdPi. Cheaper Promontory 21 cards exist in China, like JGINYUE’s at around $58 and LEKUO’s at around $89, but VideoCardz notes they have no OCuLink port. If you need the USB-A ports, WisdPi. If you want the cheapest full combo from a brand with a return desk, the ESP4B.

How much does it cost?

$135.90 in the US right now, down from a regular price of $169. Minisforum’s UK store has it at £129 (regular £159) shipping from a Hong Kong warehouse, and the EU store at €149 (regular €179), all as of October 21, 2026. Shipping is expected in late October. Minisforum backs it with a two-year warranty, a 30-day money-back window and free shipping.

What you don’t get is a list of supported systems, a power draw figure or a word on booting from the card, so plan on it as data storage until somebody confirms more. And if you’re buying it to feed a NAS or a Proxmox box, remember that every drive on it shares one 8 GB/s link.