• IT that grows your business

  • 15th March 2023

IBM i Application Development

application development - IBM i Application Development

IBM i Application Development

800 500 Finley Austin

IBM i Application Development

IBM i (formerly known as AS/400) is a platform for business computing that provides a robust and reliable environment for running applications. IBM i application development involves creating and maintaining software applications that run on the IBM i platform.

For decades, applications have been developed on what is now called the IBM i. In the 80’s there were many applications developed to run specifically on the IBM midrange platform each specific to the industry they were developed for.

These applications have been enhanced over the years to introduce new functionality and to meet regulatory rules.

application development 2 768x480 - IBM i Application Development

Many applications have been written from scratch where companies bought IBM hardware and then developed the systems they needed on those platforms.

There are therefore hundreds of IBM i applications running legacy applications in the UK all developed over a period of 40+ years.


The predominant programming language of the IBM i is RPG (Report Program Generator). RPG programs reading/writing/updating the native IBM i database DB2, deliver incredible processing speeds on a system that is renowned for its reliability.

RPG was introduced in 1959 but RPG II was the language of the S/3X machines that were the predecessors to the AS/400. RPG II was/is a programming language that used the program cycle where the system would control the logic of reading records from files.

Did you know?

  • RPG was preceded by a language called FARGO which was also a Report Generator language. (Wikipedia)
  • RPG III was introduced for the S/38 and was the main language of the AS/400 (although renamed RPG400).
  • The main text editor for the AS/400 was SEU (Source Entry Utility) – it allows developers to create, modify, and compile RPG, COBOL, and CL source code.

Other development tools on the system include:

  • SDA (screen Design Aid) was a tool for developing and designing user interfaces for data entry and enquiry.
  • RLU (report layout utility) was a tool for developing and designing reports for printing.
application development 3 768x480 - IBM i Application Development


1994 saw the release of RPG IV and RPGLE, this iteration of RPG introduced the first change in RPG moving away from fixed format code to free format. It took until 2013 before a truly free-format RPG was released by IBM.

Even though RPG has continued to evolve over the years with more built in functions, SQL functions and the capability to link to Java objects, code that was written in RPG II 40 years ago will still run on the platform today alongside code written in free format.


Together with updates to RPG, IBM introduced Rational Developer for i (RDi) in 2008: An integrated development environment (IDE) that provides a comprehensive set of tools for developing IBM i applications. RDi supports several programming languages, including RPG, COBOL, Java, CL and SQL. This tool effectively replaced SEU on the AS/400.

Whatever iteration of RPG your legacy systems are written in and whatever development tools you use, KFA have extensive experience of development on the IBM i with a team of staff who either grew up coding RPG II and have coded everything in between or started recently learning the latest version.  

Richard Austin

KFA Connect – Director

15th March 2023

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