The debugger consists of two parts: A main debugger image
    (DEBUGSHR.EXE) that contains most of the debugger code and
    a smaller kernel debugger image (DEBUG.EXE). This separation
    reduces potential interference between the debugger and the
    program being debugged and also makes it possible to have a
    multiprocess debugging session.

    When you start the debugger, a process is created to run the main
    debugger.

    In a multiprocess debugging session, each program being debugged
    runs in a separate process. Each process that is running one or
    more images under debugger control is also running a local copy
    of the kernel debugger. The main debugger, running in its own
    process, communicates with the other processes through their
    kernel debuggers.

    Although all processes of a multiprocess session must be in
    the same job, they do not have to be related in a particular
    process/subprocess hierarchy. Moreover, the program images
    running in separate processes do not have to communicate with
    each other.