In 1964 only large mainframe computers existed, each with its own separate set of users. If you were lucky the computer was timeshared, but even then you could not go far away since the terminals were hardwired to it or connected by local phone line. Moreover, if you wanted data from another computer you moved it by tape and you could forget wanting software from a different type of computer. Thus, most users were tied by their computer and terminal to a very restricted enviornment.Today, in 1985, your terminal could well be a microcomputer networked with a very large, worldwide collection of other computers. You can obtain data and software from all these computers relatively easily with room for improvement) or, where convenient, use the software and data on its home computer by remote access, computer to computer.This change, which has occurred over the past 20 years, is in part a massive and evolutionary change in computer technology, and in part a modest and revolutionary change in communications technology. The revolution in communications started with an experiment in computer networking, the ARPANET, and grew into a communications revolution called packet switching. Today virtually all the world is linked by packet switched communications service so that any terminal can access almost any computer in the world. This packet switched data network has grown up independent of the telephone network, but over the next 20 years the basic fabric supporting all switched services (data, telephone and video) appear likely to become converted to packet switching, completing the revolution.