Editing IBM RPG II (section)

==Features==
RPG II is a fixed-format programming language, which means that code must be placed in exact column locations in order to generate correct results. There are eight different specification types, and separate coding forms are used to write each, and a special debugging template<ref name=template>[http://www.computerhistory.org/collections/catalog/X957.88J "IBM RPG Debugging Template"], Computer History Museum</ref>  used as an aid to read program printouts.

Every RPG II program executes within an implied loop, the [[main loop|program cycle]], which applies the program successively to every record of a file - this is documented via a "Logic Flow" diagram on the debugging template.<ref name=template/> Each record (individual punched card) would be compared to each line in the program, which would act upon the record, or not, based upon whether that line had an "indicator" turned "on" or "off" — from a set of logical variables numbered 01–99 for user-defined purposes, or other smaller sets based upon record, field, or report processing functions. Special variables such as UDATE, UYEAR, PAGE, and so forth, are filled when the program begins or when page overflow occurs, even though there is no explicit instruction for these activities.  Total calculations and output are done at "total time," after the detail cycle when L1/LR has been set on by fixed logic.

The concept of RPG's program cycle fitted neatly with a cyclical machine that read cards, summarised their contents and prints a result, rather like a [[tabulating machine]]. The language was extended to handle other input and output devices and provides a fast and efficient method of programming.

Devices such as the workstation (WORKSTN), the keyboard (KEYBORD), or the console (CONSOLE) do not have a fixed number of records at the beginning of the job and therefore, in order to incorporate the fixed-logic RPG "Last Record" cycle, the LR indicator can be set on with a SETON instruction.  LR cannot be set off.

RPG II did not evolve much from the 1977 implementation on the System/34 to 2000 when the [[Advanced/36]] was discontinued from marketing. Changes that were made from the 1970s version included the IFEQ/IFNE/IFGT/IFGE/IFLT/IFLE and END grouping. Also, the call/parm to be able to call external subroutines. Another change was that for internal subroutines, you no longer had to put SR in columns 7 and 8 of the C (calculation) specs.

Third-party providers sold more than 200 different assembler subroutines that could be used by System/36 and Advanced/36 programmers to exceed RPG II limitations. Some of the limitations of RPG II on the System/3, 32, 34 and 36 including the Advanced/36 was the 64K limit and the number of files you could have in a program. So if you had a lot of programming lines or had large arrays, it was easy to exceed the 64,000 bytes of object code. However, RPG II running on the AS/400 and its follow on iseries and IBM i (those running OS/400 or i5/OS in what is called S/36E (execution environment)) those limits (the 64K bytes and the number of files) were either greatly expanded or removed.