The Wait Is Over: Meet the LEKUO Southbridge Mini — One PCIe Slot, Ten Interfaces
The bottom line: The PR51RX3 packs two 10Gbps Type-C ports, three 5Gbps USB-A ports, one 2.5GbE port, and four SATA ports into a single 110 × 68 mm card, all connected through a single PCIe x1 upstream link.
This isn't just another expansion card that adds a couple of USB ports. It's designed to bring the functions of an entire southbridge into a single PCIe card.
1. Ten Ports, Clearly Explained
The upstream interface is PCIe Gen4 x1, offering up to 16Gbps of theoretical unidirectional bandwidth. It is backward-compatible with PCIe Gen3, Gen2, and Gen1.
The card can be installed in PCIe x1, x4, x8, or x16 slots.
2. Why Do We Call It a "Southbridge Mini"?
The name isn't just marketing.
Long-time PC builders will remember the southbridge chip on older motherboards. It handled peripheral connectivity, including USB, SATA, networking, and audio.
Over time, Intel and AMD integrated or redistributed these functions across the CPU and the Platform Controller Hub (PCH), and the traditional concept of a separate southbridge gradually faded away.
But the need for peripheral connectivity hasn't disappeared.
Your PC may still need more USB ports, more SATA connections, or an additional network interface. The available motherboard connections are limited, and once they're all occupied, that's it.
The PR51RX3 brings these functions back in a different form.
Through a single PCIe x1 connection, it uses the RTL9151 chipset as a compact peripheral hub, taking one PCIe lane upstream and expanding it into ten interfaces downstream.
That's what we mean by "Southbridge Mini": its functional role, not just a nickname.
3. 16Gbps Upstream: How Do Ten Ports Share the Bandwidth?
This is an important point to understand before buying the card.
All ten interfaces share the same 16Gbps upstream bandwidth.
That's the physical bandwidth limit of PCIe Gen4 x1, not a product shortcoming.
So, is it enough? That depends on how you use the card.
- Running one 10Gbps Type-C connection: It can use the available upstream bandwidth with minimal interference from other active devices.
- Running four SATA SSDs simultaneously: Each drive can deliver sequential read speeds of 448–478 MB/s. Combined, the four drives push the shared upstream connection close to its practical limit.
- Running all nine storage interfaces simultaneously: The devices compete for upstream bandwidth, so individual transfer speeds will decrease depending on the workload.
In other words, the PR51RX3 is ideal for setups where multiple devices stay connected, but not every device needs maximum throughput at the same time.
NAS systems, media workstations, and PCs with numerous peripherals are good examples.
If you need all ten interfaces to deliver their maximum speeds simultaneously, a single x1 card isn't the right solution. You'll need more PCIe bandwidth.
4. Real-World Testing: Putting the Interfaces to Work
LEKUO conducted internal testing across all ten interfaces. Here's what we found.
4 × SATA Gen 3: Four Drives Running Simultaneously
Sequential read speeds: 448–478 MB/s per drive
All four SATA drives were tested simultaneously using CrystalDiskMark.
The results were:
448.38 / 456.50 / 462.71 / 478.07 MB/s
With real-world SATA 6Gbps sequential read speeds typically approaching 500 MB/s, all four drives delivered strong performance at the same time.
2 × Type-C (10Gbps): 883 / 907 MB/s
Sequential read speeds: 883.71 MB/s and 907.94 MB/s
Both Type-C ports delivered sequential read speeds close to the practical limit of a USB 3.2 Gen 2 10Gbps connection.
Type-C Reversible Plug Test: 875 / 896 MB/s
USB Type-C supports reversible insertion, but performance can vary between implementations.
In our testing, the ports delivered 883 / 907 MB/s with the connector in one orientation and 875 / 896 MB/s after reversing it.
The differences fall within a normal range of performance variation, indicating consistent results in both orientations.
The CC logic and internal MUX switching are working as intended.
3 × USB-A (5Gbps): 421–426 MB/s
Sequential read speeds: 421–426 MB/s
The three USB-A ports achieved:
424.24 / 426.04 / 421.61 MB/s
With a practical throughput ceiling of approximately 440 MB/s for a 5Gbps USB connection, all three ports performed close to the expected limit.
All Nine Storage Interfaces Online Simultaneously
We connected storage devices to all nine storage-capable interfaces:
- 4 × SATA
- 3 × USB-A
- 2 × Type-C
All nine devices were connected and tested simultaneously.
Every drive was recognized normally, with no drives dropping offline during the test.
Full-Load Temperature: 45.2°C on the Heatsink Surface
Under full-load testing, the heatsink surface measured 45.2°C, with a maximum recorded temperature of 49.7°C.
The card uses passive cooling with no fan. Under these test conditions, the heatsink was warm to the touch, without requiring active airflow from an onboard fan.
5. Compatibility: Seven Motherboards and Multiple Operating Systems
We tested the PR51RX3 across seven motherboards and several operating system environments.
On fnOS, our NAS testing confirmed that all drives connected through SATA and USB were recognized normally, without requiring additional drivers.
For DIY NAS builders, this is more than a specification on paper. It's a practical advantage.
The specifications list support for Windows and Linux. SATA uses AHCI 1.3.1, while USB is compatible with xHCI 1.2 / 1.1. These standard interfaces fall within the scope of native operating system driver support, which helps explain the straightforward installation experience.
6. Who Can Benefit Most from the PR51RX3?
Mini PCs and ITX builds
Space and expansion slots are limited. One PCIe x1 connection provides ten interfaces, making the most of a scarce expansion resource.
Older motherboards
If your motherboard has too few USB ports or only a couple of SATA connections, the PR51RX3 offers an expansion option without replacing your entire platform.
DIY NAS systems
Add four SATA drives and gain a 2.5GbE network interface at the same time. For NAS systems still running on Gigabit Ethernet, the additional network bandwidth can be particularly useful.
Soft routers and workstations
Add Ethernet and multiple USB connections in one card instead of installing several separate expansion cards or relying on a stack of hubs.
Peripheral-heavy workstations
Give capture devices, card readers, security dongles, and external drives their own connections, reducing the need to repeatedly unplug and reconnect devices.
7. Three Things to Know Before Buying
1. All Ten Interfaces Share 16Gbps of Upstream Bandwidth
When multiple devices transfer data simultaneously, they share the available bandwidth.
This is a physical limitation of the PCIe x1 connection. Consider your actual workload before purchasing.
2. Two USB-A Ports Require an Optional Cable
Of the three USB-A ports, one connects directly through the expansion card's bracket.
The other two require a 19-pin internal USB header to dual USB-A female cable to route the connections to the front of the PC case.
This cable is optional, so remember to add it to your order if you need it.
【Image 13｜19 针转双 USB-A 母座线的产品图片，标注为选配配件】
3. SATA Data and Power Cables Are Not Included
The card provides four SATA connectors, but you'll need to prepare your own SATA data cables and drive power connections.
Before installation, make sure your power supply has enough available SATA power connectors for all the drives you plan to install.
The card measures 110 × 68 mm and weighs approximately 80 g. It installs in a standard expansion slot and includes a short bracket option, making it suitable for smaller PC cases as well.
Final Thoughts
One PCIe x1 connection.
Two 10Gbps Type-C ports. Three 5Gbps USB-A ports. One 2.5GbE network port. Four SATA ports.
Ten interfaces. One card. One upstream connection.
The LEKUO PR51RX3 Southbridge Mini is now available.
For users who need more connectivity without replacing their motherboard or filling every available expansion slot, it's a practical way to bring more peripheral I/O into a compact system.
#LEKUO #PCIe #ExpansionCard #NAS #PCHardware
🛒：https://lekuo.shop/products/lekuo-southbridge-mini-pcie-x1-to-10-port-multi-function-expansion-card