The invention provides a new and improved system for transferring information between a host system and a terminal system. A digital data processing system includes a host computer system which runs processors and a terminal system which is connected to the application host computer system over a communication link. The terminal system includes one or more virtual terminals each of which allows an operator to enter information and allows output information to be displayed. The association between a terminal device and an application process is a session. Initially, a session is selected by means of a command transferred over the communications link. Thereafter, information, associated with the selected session, may be transferred over the communication link. This may continue until another session is selected. This transfer system minimizes the amount of control information which is required to identify the particular session with which data being transmitted over the communications link is associated. Once a session is selected, it remains selected until another session is selected, after which the data transmitted is associated with the newly selected session.
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