The LAN91C100FD is designed to facilitate the implementation of first generation Fast Ethernet adapters and connectivity products. For this first generation of products， flexibility dominates over integration. The LAN91C100FD is a digital device that implements the MAC portion of the CSMA/CD protocol at 10 and 100 Mbps， and couples it with a lean and fast data and control path system architecture to ensure the CPU to packet RAM data movement does not cause a bottleneck at 100 Mbps.

　　Total memory size is 128 Kbytes， equivalent to a total chip storage （transmit plus receive） of 64 outstanding packets. The LAN91C100FD is software compatible with the LAN9000 family of products and can use existing LAN9000 drivers （ODI， IPX， and NDIS） in 16 and 32 bit Intel X86 based environments.

　　Memory management is handled using a unique MMU （Memory Management Unit） architecture and a 32-bit wide data path. This I/O mapped architecture can sustain back-to-back frame transmission and reception for superior data throughput and optimal performance. It also dynamically allocates buffer memory in an efficient buffer utilization scheme， reducing software tasks and relieving the host CPU from performing these housekeeping functions. The total memory size is 128 Kbytes （external）， equivalent to a total chip storage （transmit and receive） of 64 outstanding packets.