Editing IBM RPG (section)

===RPG II===
{{main|RPG II}}
''RPG II'' was introduced about 1969 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.  RPG II was also available for larger systems, including the [[IBM System/370]] mainframe running [[DOS/VSE]] (then [[VSE/SP]], [[VSE/ESA]], and [[z/VSE]]). [[International Computers Limited|ICL]] also produced a version on its [[ICL VME|VME/K]] operating system.

In the early days of RPG, its major strength was the ''program cycle''. A programmer would write code to process an individual record, and the program cycle would execute the change against every record of a file, taking care of the control flow. At that time 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". The indicator consisted of a set of logical variables numbered 01–99 for user-defined purposes, or other smaller sets based upon record, field, or report processing functions. The concept of level breaks and matching records is unique to the RPG II language, and was originally developed with card readers in mind. The matching record feature of the cycle enabled easy processing of files having a header-to-detail relationship. RPG programs written to take advantage of the program cycle could produce complex reports with far fewer lines of computer code than programs written in [[COBOL]] and other business-centric languages.  
 
The program File Specifications, listed all files being written to, read from or updated, followed by [[Data definition specification|Data Definition Specification]]s containing program elements such as Data Structures and dimensional arrays, much like a "Working-Storage" section of a COBOL program. This is followed by Calculation Specifications, which contain the executable instructions. Output Specifications can follow which can be used to determine the layout of other files or reports. Alternatively files, some [[data structure]]s and reports can be defined externally, mostly eliminating the need to hand code input and output ("[[Input/output|I/O]]") specifications.