The DP83820 Gigabit Fiber Ethernet to PCI Bus Adapter is a network interface card (NIC) that allows a computer or server to connect to a network via Gigabit Ethernet using fiber-optic cables. The DP83820 is a specific model of Ethernet PHY (Physical Layer) controller made by Texas Instruments. It's commonly used in network devices to manage the physical layer of Ethernet communication, providing high-speed networking over fiber-optic connections, usually at 1 Gbps (Gigabit Ethernet speeds).