While the RTL8139 (original PCI version) is limited to 100 Mbps, it remains fully functional for web browsing and light streaming. However, on a Gigabit network, the older chip becomes a bottleneck. The PCI-E 810x series, by contrast, can achieve 800–940 Mbps in real-world transfers on Windows 10, provided the driver’s checksum offloading is enabled. Disabling “Large Send Offload” (LSO) sometimes improves stability on buggy router firmware.
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There is no official one. Realtek EOL’d the RTL8139 in 2013. The last official driver was for Windows 7/8. The driver you find under the "810x" package is a generic NDIS driver that offers basic functionality.
The Realtek RTL8139 is a PCI-E (Peripheral Component Interconnect Express) Gigabit Ethernet adapter that supports data transfer rates of up to 1 Gbps. This chip was designed to provide high-speed network connectivity for desktops, laptops, and servers. With its compact design and low power consumption, the RTL8139 quickly gained popularity among system manufacturers and users alike.
For the family of network controllers, official support from Realtek typically ended with Windows 7 or 8.1. However, you can still get these devices working on Windows 10 using legacy drivers or manual installation methods.