Method of control for re-entrant programs

The use of multiprogramming and multiprocessing raises a question as to the number of copies of a routine needed in memory for multiple concurrent use. In the case where two or more scientific programs are in core at the same time, each needing the use of a SINE routine, a private copy can be provided for each program's own use, or one copy can be loaded for all to use. A message processing program that services multiple terminals can run into a situation where message A interrupts the processing of message B and because of priority considerations, message A must be processed immediately by the program. Again, the question of how many copies of the program are required in core occurs. Finally, a multiprocessing configuration with two or more computers sharing a common core memory may each be using the FORTRAN compiler. Each computer could have its own copy of the compiler or a single copy of the compiler could be executed by all computers concurrently. Intuitively, the provision of one copy of the routine or program appears more elegant.