You can use the debugger in two configurations, default or
    multiprocess. Use the default configuration to debug a program
    that normally runs (without the debugger) in only one process.
    Use the multiprocess configuration to debug a program that
    normally runs in more than one process. The configuration depends
    only on the definition of the logical name DBG$PROCESS, as
    indicated in the following table:

    DBG$PROCESS
    Definition:            Configuration:

    DEFAULT or undefined   Default
    MULTIPROCESS           Multiprocess

    Note that the debugging configuration does not depend on whether
    the program runs in one or several processes. Rather, the current
    definition of DBG$PROCESS determines whether debuggable images
    running in different processes can be controlled from the same
    debugging session.

    Before starting the debugger, enter the DCL command SHOW LOGICAL
    DBG$PROCESS to determine the current definition of DBG$PROCESS
    and the resulting debugging configuration.