A long time ago, a typical enterprise installation used only one networking protocol to access the applications running on its computers. Exactly which protocol was used depended almost entirely on which manufacturers' hardware and operating system were installed. If user installed IBM equipment user used SNA, DEC installations used DECNet, most UNIX installations used TCP/IP, and so on. More recently, the choice of networking protocols has been determined by the applications that the customer has chosen to install. This has led inevitably to a proliferation of networking protocols within a single physical network.