Logical-terminal queues

Using a message queue for received input messages or for pending output messages enables an application program to be independent of the arrival time and message transmission. Because this message queue is associated with a logical terminal, rather than with a physical terminal, the message queue can be moved from device to device, independent of the application program. The message queue can even be moved among device classes.

Logical terminals provide stability for application programs. Regardless of how the physical terminal network changes, the application programs remain insensitive to these changes.

The application program interface to a logical terminal is conceptually the same as that for the database system:
  • GU calls retrieve message segments from a queue.
  • ISRT calls insert message segments to a queue.