The LEKUO SouthBridge Mini (Model: PR51RX3) is an all-in-one PCIe Gen4 x1 expansion card powered by the high-performance Realtek RTL9151 chipset. Designed for desktop PCs, workstations, servers, and embedded platforms, it transforms a single PCIe 4.0 x1 slot into 10 high-speed interfaces—combining multi-gigabit networking, fast USB connectivity, and multi-drive SATA storage on a single compact card.
Key Features
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One Chip, 10 Interfaces: Expands a single PCIe x1 slot into 2 x USB-C (10Gbps), 3 x USB-A (5Gbps), 1 x 2.5GbE Ethernet port, and 4 x SATA III (6Gbps) ports.
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PCIe Gen4 x1 Upstream Bandwidth: Delivers up to 16Gbps total upstream bandwidth (8Gbps in a PCIe 3.0 slot). All 10 ports share a dynamic bandwidth pool with real-time load distribution.
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Universal Slot Compatibility: Fits standard PCIe X1, X4, X8, and X16 slots. No motherboard bifurcation or BIOS setup required. Backward compatible with PCIe Gen3, Gen2, and Gen1.
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Broad OS Compatibility & Driverless Setup: True plug-and-play operation on Windows 11, Windows 10, and Linux without requiring additional driver installation.
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Compact Form Factor: Board dimensions of 110 x 69mm with both standard and 2U low-profile brackets included, ideal for compact ITX cases, 2U rackmount servers, and custom enclosures.
Built for Almost Any Platform
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Desktop & ITX PCs: Adds dual 10Gbps USB-C ports and a 2.5G Ethernet connection for high-speed peripherals and low-latency networking.
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Industrial PCs & Equipment: Provides multiple SATA storage interfaces and high-speed USB ports with reliable stability in demanding environments.
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Servers & Network Equipment: Upgrades server infrastructure with 2.5G networking and external storage backup capabilities.
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Embedded Devices: Compact multi-protocol connectivity delivering maximum capability in space-constrained installations.
High-Speed Core Architecture
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RTL9151 High-Performance Chipset: Integrated controller managing simultaneous high-speed data transfer across storage, networking, and USB subsystems.
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PCIe Gen4 x1 Upstream Interface: Up to 16Gbps one-way upstream bandwidth; backward compatible with Gen3, Gen2, and Gen1.
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Advanced Hardware Features: Supports ASPM L0s/L1 low-power states, MSI/MSI-X interrupts, AER (Advanced Error Reporting), LTR (Latency Tolerance Reporting), and VC (Virtual Channels).
Detailed Interface Breakdown
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2 x USB-C (10Gbps): Reversible Type-C ports with internal signal routing (MUX). Features CC logic supplying 5V/3A port power to connected devices (standard port power; not PD fast charging).
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3 x USB-A (5Gbps): 1 x external rear USB 3.0 Type-A port, plus an internal 19(20)-pin USB 3.0 header supporting 2 additional USB-A ports via adapter cable (sold separately). Fully compatible with BC1.2 charging and backward compatible with USB 2.0 / 1.1.
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1 x 2.5GBASE-T Ethernet: Built-in PHY supporting 10/100/1000M/2.5G auto-negotiation, Auto MDI/MDI-X (no crossover cable required), 16KB jumbo frames, Wake-on-LAN, and Energy-Efficient Ethernet. (Note: Router or switch must also support 2.5G to achieve 2.5G network speeds).
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4 x SATA III (6Gbps): Backward compatible with SATA II / I. Supports AHCI 1.3.1, NCQ (Native Command Queuing), and SATA power management. Drives share the 16Gbps upstream bandwidth; a single SATA SSD can operate near full interface speed.
16Gbps Shared Bandwidth Pool
All downstream ports (1 x 2.5G Ethernet + 4 x SATA + 2 x USB-C + 3 x USB-A) share a single PCIe 4.0 x1 (16Gbps) bandwidth pool. The intelligent allocation architecture dynamically balances bandwidth based on real-time device load, maintaining stable operation across multiple active peripherals and maximizing throughput on single-port tasks.
Installation Notes & Compatibility
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Operating System Support: Windows 11, Windows 10, Linux, and other major operating systems.
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Installation Safety: Shut down the PC and disconnect it from power before inserting the card into a PCIe slot (PCIe slots do not support hot-plugging).
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Hot-Plugging: Once the card is installed, USB peripherals and RJ45 network cables can be plugged in or unplugged at any time. SATA storage drives should only be connected or disconnected after shutting down the PC.
Specifications
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Brand: LEKUO
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Product Name: LEKUO SouthBridge Mini
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Model: PR51RX3
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PCIe Standard: PCIe Gen4 X1 (backward compatible with Gen3 / Gen2 / Gen1)
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Compatible Slots: PCIe X1, X4, X8, X16
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Output Interfaces: 2 x USB-C (10Gbps), 3 x USB-A (5Gbps, adapter cable sold separately), 1 x 2.5GbE Ethernet, 4 x SATA III (6Gbps)
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Dimensions: 110 x 69 mm
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Weight: Net: 80g | Gross: 250g
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Packaging Dimensions: 173 x 140 mm
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OS Support: Windows 10 / 11, Linux
Package Contents
- 1 x LEKUO SouthBridge Mini Expansion Card (PR51RX3)
- 1 x 2U Low-Profile Bracket
- 1 x User Manual
URL:https://cn.lekuo.com/uploadfile/upload//data/upload/image/RTL8125.zip
Q: What kind of expansion card is the PR51RX3, and what ports does it add?
A: The PR51RX3 is an all-in-one multi-function "SouthBridge" expansion card based on the Realtek RTL9151 bridge chipset. It expands a single PCIe x1 upstream lane into a total of 10 downstream ports: 2 x USB 3.2 Gen 2 Type-C (10Gbps), 3 x USB 3.2 Gen 1 Type-A (5Gbps), 1 x 2.5GBASE-T RJ45 Ethernet port, and 4 x SATA Gen 3 (6Gbps) ports. In short, installing a single card simultaneously adds high-speed USB, 2.5G wired networking, and SATA storage expansion—making it ideal for desktop PCs, workstations, servers, soft routers, and NAS platforms.
Q: With only a PCIe x1 upstream lane, is the bandwidth sufficient? Will connecting all devices cause bottlenecks?
A: The PR51RX3 utilizes a PCIe Gen4 x1 upstream link providing up to 16Gbps (approx. 2GB/s) of unidirectional bandwidth, and is backward compatible with Gen3, Gen2, and Gen1. When installed in a PCIe 3.0 slot, x1 bandwidth is approximately 8Gbps (approx. 1GB/s). All downstream ports share this single upstream channel, meaning not all 10 ports can reach peak theoretical speeds simultaneously—this is an inherent architectural design of bridge cards rather than a defect. In real-world workloads, peripherals typically serve different roles (e.g., 2.5G LAN for local transfers, USB-C for an external SSD, and SATA for mass storage drives), so typical concurrent usage remains smooth and well within bandwidth limits. Bottlenecks will only occur during extreme multi-device scenarios like simultaneous multi-drive massive file transfers alongside saturated multi-gigabit networking.
Q: What is the real-world speed of the 2.5G Ethernet port, and what are the requirements for cables and switches?
A: The Ethernet port supports 10/100/1000M/2.5G auto-negotiation and complies with the IEEE 802.3bz standard. Real-world TCP throughput typically reaches 2.3–2.4Gbps (approx. 280–290MB/s), which is 2.5 times the speed of standard gigabit LAN. For cabling, Cat5e cables are sufficient for stable 2.5G negotiation over typical home distances, though Cat6 or higher is recommended where possible. The connected switch or router port must also support 2.5GbE or higher speeds; connecting to a standard gigabit port will automatically negotiate at 1Gbps. It also supports 16KB Jumbo Frames, Wake-on-LAN (WoL), RSS multi-queue, ARP/NS protocol offloading, and IEEE 802.3az Energy-Efficient Ethernet.
Q: Are both Type-C ports 10Gbps? Can they power phones or external drive enclosures?
A: Yes, both USB 3.2 Gen 2 Type-C ports operate at 10Gbps, comply with the xHCI 1.2 specification, feature reversible plug detection with internal MUX switching, and include CC logic to provide standard 5V/3A port power. When connected to a 10Gbps external SSD enclosure, sequential read/write speeds typically reach 900MB/s–1GB/s. They can also connect to smartphones and tablets for charging and data transfer, as well as high-speed card readers and 4K capture devices. Please note: output current is limited by the PCIe slot's power budget, so avoid connecting multiple high-draw bus-powered devices simultaneously.
Q: What are the speeds of the three USB-A ports? Do they support fast charging?
A: The three USB 3.2 Gen 1 Type-A ports operate at 5Gbps, comply with xHCI 1.1, and are backward compatible with USB 2.0 and 1.1, making them ideal for keyboards, mice, flash drives, printers, webcams, and wireless dongles. They support the BC 1.2 battery charging specification to charge phones, wireless headphones, and other accessories. The USB controller supports UAS, BOT, UAC, UVC, and HID protocols (audio devices, cameras, and microphones work plug-and-play), features independent port power control and overcurrent protection, and supports remote wake-up and hot-plug wake-up, with support for up to 64 cascaded devices per port.
Q: Can the 4 SATA ports connect mechanical hard drives for storage? Do they support NCQ, hot-plugging, and RAID?
A: Yes. All 4 SATA Gen 3 ports run at 6Gbps, are backward compatible with Gen2 and Gen1, and comply with AHCI 1.3.1. They support Native Command Queuing (NCQ), Partial/Slumber power management, and speed auto-negotiation, making them well-suited for 2.5-inch and 3.5-inch HDDs or SATA SSDs used for backup, bulk storage, or download caching. RAID arrays are managed via operating system software (such as Windows Storage Spaces, Linux mdadm, or ZFS), as the card does not feature hardware RAID. For safety and data integrity, shutting down the system before connecting or disconnecting drives is recommended.
Q: Does the card require driver installation? Does it support Windows, Linux, and macOS?
A: It officially supports Windows and Linux (macOS is not supported; Mac users should not purchase this card). The USB and SATA controllers operate on standard OS-level xHCI and AHCI protocol stacks and are automatically recognized on Windows 10/11 and mainstream Linux distributions. The 2.5G Ethernet controller may require a driver on certain operating systems to enable full performance and features; you can download the driver directly from this page. Installing it enables advanced features such as Jumbo Frames, WoL, and RSS. Linux users should ensure their kernel includes the appropriate network driver module.
Q: My motherboard only has an x1 slot available. Can I use this card? Does it fit compact cases and 2U servers?
A: Absolutely. The card features a standard PCIe x1 edge connector, allowing it to be installed in PCIe x1, x4, x8, or x16 slots (longer slots are fully compatible). This is one of its biggest advantages: putting that commonly unused x1 slot to full use. With compact board dimensions of only 110 x 68mm, it comes with an included low-profile bracket, fitting ITX mini chassis, HTPCs, soft router cases, and 2U/3U rackmount servers. A 19-pin USB 3.0 internal header adapter cable is also supported for routing front-panel USB ports (subject to package contents).
Q: How should I choose between this card and the Lekuo "SouthBridge Max" PB65MX3?
A: It depends on your primary expansion needs: choose the SouthBridge Max PB65MX3 if you need multiple M.2 NVMe SSD slots. It uses a PCIe 4.0 x4 upstream link and provides 4 x M.2 NVMe slots + 4 x SATA + 4 x USB (including a 20Gbps USB-C port), focusing on high-density storage expansion. Choose the SouthBridge Mini PR51RX3 if you want diverse I/O types using minimal lanes. It requires only a single PCIe x1 slot to simultaneously deliver 5 x USB ports, 1 x 2.5G LAN port, and 4 x SATA ports without occupying a valuable x16 or x4 slot. In summary: choose PB65MX3 for NVMe SSD pooling; choose PR51RX3 to add network, USB, and SATA ports using a spare x1 slot.
Q: What should I keep in mind during daily use?
A: Keep these four points in mind: 1. Bandwidth sharing — all 10 downstream ports share the upstream PCIe x1 lane, meaning multiple ports running under peak loads will share available throughput; 2. Power delivery — the card draws power directly from the PCIe slot, where the x1 slot's power budget is limited. If connecting multiple 3.5-inch mechanical drives alongside high-draw USB-C devices, ensure your system power supply is adequate and consider dedicated drive power; 3. Thermal airflow — the expansion card generates heat during heavy workloads, so ensure basic case ventilation; 4. Feature scope — this card provides USB, 2.5GbE LAN, and SATA connectivity; it does not include M.2 NVMe slots and does not support macOS. Please verify compatibility before purchasing.
