08/22/83  External Storage

External storage (PL/I external variables and FORTRAN common blocks)
is usually allocated by the dynamic linker when a program is run.  The
size and initial value is determined by information associated with
the first procedure that references the storage.  If another procedure
subsequently references the same storage, the linker ignores any
associated initialization value.  If the size indicated is larger than
that allocated, the linker signals linkage_error.  In this case, the
program cannot be restarted.


There are four ways of ensuring that the correct sizes and initial
values are allocated:

   1) Make all declarations for an external variable identical.
      (Recommended)
   2) Bind together all procedures that reference the same external
      storage.
   3) Use the set_fortran_common command before running the program,
      giving it the names of all procedures containing relevant
      information about external storage (largest sizes, correct
      initial values, etc.) (Warning--continued operation with PL/I
      procedures is not guaranteed).
   4) Compile together all FORTRAN programs referencing the same common
      blocks.  The list_external_variables command can be used to
      display information about external variables or common blocks
      already allocated.

See allocation_storage.gi for general information on system storage
areas.      


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved