RPG Language Evolution

RPG II was introduced with the System/3 series of computers. It was later used on System/32, System/34, and System/36, with an improved version of the language. International Computers Ltd also produced a version on its VME/K operating system

RPG III was created for the System/38 and its successor the AS/400 (a mid-range machine). RPG III significantly departed from the original language, providing modern structured constructs like IF-ENDIF blocks, DO loops, and subroutines.

DE/RPG or Data Entry RPG was exclusively available on the IBM 5280 series of data-entry workstations in the early 80s. It was similar to RPG III but lacking external Data Descriptions (DDS) to describe data(files) like on the System/38 and its successors. Instead, the DDS part had to be included into the RPG source itself.

RPG/400 with a much cleaner syntax, and tighter integration with the integrated database. This language became the mainstay of development on the AS/400, and its editor was a simple line editor with prompt templates for each specification (type of instruction).

RPG IV (aka RPGLE, aka RPG/ILE) was released in 1994 and the name, officially, was no longer an initialism. RPG IV offered a greater variety of expressions within its new Extended Factor-2 Calculation Specification.