Winsock is an open-standard network API for Microsoft Windows developed by over 30 network hardware and software providers, including Microsoft, Novell, 3Com, IBM, Sun, HP and DEC. The Winsock API is contained in a DLL that is included on all Windows operating systems. Winsock 2 is an extension to the Winsock API that adds various performance optimizations as well as all the functionality required in order to work with emerging network technologies. Under Windows NT, 2000 and XP, Winsock 2 takes advantage of operating-system level networking support such as I/O completion ports to enable maximum scalability and communications efficiency.