The 21140-based 10100Mbps Fast Ethernet Controller is a network interface card (NIC) used in many computers to provide wired Ethernet connectivity. The name suggests that it's based on the National Semiconductor 21140 chip, which supports 10/100 Mbps Ethernet speeds (Fast Ethernet). The driver allows your computer to communicate with the Ethernet hardware, enabling wired networking.

The Windows driver for the 21140-based Ethernet controller is software that allows Windows to recognize and communicate with the NIC, allowing the device to work for internet access, local networking, file sharing, etc.