The ILE RPG compiler supplies part of the logic for an RPG program. For a cycle-main procedure, the logic the compiler supplies is called the program cycle or logic cycle. The program cycle is a series of ordered steps that the main procedure goes through for each record read.
The information that you code on RPG IV specifications in your source program need not explicitly specify when records should be read or written. The ILE RPG compiler can supply the logical order for these operations when your source program is compiled. Depending on the specifications you code, your program may or may not use each step in the cycle.
Primary (identified by a P in position 18 of the file description
specifications) and secondary (identified by an S in position 18 of
the file description specifications) files indicate input is controlled
by the program cycle. A full procedural file
(defined using a free-form DCL-F statement, or identified by an F in
position 18 of the file description specifications) indicates that
input is controlled by program-specified calculation operations (for
example, READ and CHAIN).