W5100 is a multifunctional Monolithic network interface chip, internal integrate a 10/100 Ethernet controller , it apply to a embedded system which is High-Integrate, high-stability, high-performance but low-cost. By using it, we can complete the internet linking without operating system supporting. W5100 compatible with IEEE802.3 10BASE-T and 802.3u100BASE-TX. W5100 internal integrate TCP/IP,MAC,PHY with full hardware control. We just need to have some simple socket programming rather than considering the control of the Ethernet when we use the W5100.