It is important to clarify that the Realtek RTL8139 and 810x family are actually Fast Ethernet controllers, limited to a maximum speed of 100 Mbps. While they are compatible with modern Gigabit networks, they cannot reach 1000 Mbps (Gigabit) speeds.
Legacy Status: These chips were developed between 1997 and 2005 and reached nearly 65% market share at their peak. Installing Drivers on Windows 10 realtek rtl8139 driver 810x family pci-e gigabit windows 10
If you see this device in your Device Manager, you are technically using Fast Ethernet (10/100). It is important to clarify that the Realtek
DEV_8139 → You have a real RTL8139 (Legacy PCI).DEV_8168 → You have a Realtek PCI-E Gigabit adapter (often mislabeled as RTL8139 in generic drivers).DEV_8100, DEV_8101, DEV_8102, DEV_8105, DEV_8106 → You have the 810x Family.