03/25/74  Load Control Groups

Load control groups control who gets logged in.
Each project is assigned to a load control group, which has
a quota of guaranteed primary load units.
When a user logs in, he is assigned "primary" status
if his load control group is not full. He gets a message
of the form
     You are protected from preemption until 1832.
which tells him how long he may keep primary status.

If a user's group is full, but the system is not full,
he may be assigned "secondary" status and receive the message

     You are subject to preemption.

This warns him that a primary user may preempt (bump) him
in order to log in, if the system is full.

Users who are preempted are given a three-minute warning
before automatic logout, which looks like this:

     **********
     From Multics: Secondary user preemption.
     You will be logged out in 3 minutes.
     **********


Login decision:
I. System is not full
   A. Group is not full --> login as primary
   B. Group is full, search primary users of same group
      1. Found primary user with expired grace --> demote him
          to secondary and login as primary
      2. No user with expired grace --> login as secondary

II. System is full
   A. Group is not full --> must be a secondary on system,
       preempt him and login as primary
   B. Group is full, search primary users of same group
      1. Found primary user with expired grace --> preempt him
         and login as primary
      2. No user with expired grace --> sorry, system full. no login.

For preemption or demotion, the user who logged in first is the
first candidate.

Secondary users are promoted to primary if a primary user
from the same group logs out. Here too, the user who logged in first
is the one who is promoted.


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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