Before the wide spread of internetworking (802.1) that led to the Internet, most communication networks were limited by their nature to only allow communications within the stations on the local network and the prevalent computer networking method was based on the central mainframe computer model. Several research programs began to explore and articulate principles of networking between physically separate networks, leading to the development of the packet switching model of digital networking. These research efforts included those of the laboratories of Donald Davies (NPL), Paul Baran (RAND Corporation), and Leonard Kleinrock at MIT and at UCLA. The research led to the development of several packet-switched networking solutions in the late 1960s and 1970s, including ARPANET and the X.25 protocols. Additionally, public access and hobbyist networking systems grew in popularity, including unix-to-unix copy (UUCP) and FidoNet. They were however still disjointed separate networks, served only by limited gateways between networks. This led to the application of packet switching to develop a protocol for internetworking, where multiple different networks could be joined together into a super-framework of networks. By defining a simple common network system, the Internet Protocol Suite, the concept of the network could be separated from its physical implementation. This spread of internetworking began to form into the idea of a global network that would be called the Internet, based on standardized protocols officially implemented in 1982. Adoption and interconnection occurred quickly across the advanced telecommunication networks of the western world, and then began to penetrate into the rest of the world as it became the de-facto international standard for the global network. However, the disparity of growth between advanced nations and the third-world countries led to a digital divide that is still a concern today.