Douglas Earl Comer is a professor of computer science at Purdue University, where he teaches courses on operating systems and computer networks. He has written numerous research papers and textbooks, and currently heads several networking research projects. He has been involved in TCP/IP and internetworking since the late 1970s, and is an internationally recognized authority. He designed and implemented X25NET and Cypress networks, and the Xinu operating system. He is director of the Internetworking Research Group at Purdue, editor of Software - Practice and Experience, and a former member of the Internet Architecture Board. Comer completed the original version of Xinu (and wrote correspondent book The Xinu Approach) in 1979. Since then, Xinu has been expanded and ported to a wide variety