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Barrett Otte
Barrett Otte

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RPG and IBM i

This is my first post to DEV to see if there are any developers on here who have messed around with IBM i before or are interested in learning what it is. Primarily, I will be focusing on the history of IBM i and the RPG programming language that has evolved with it.

At my current workplace, I noticed this ominous green and black screen on numerous older developers' monitors. Shortly after, I found out that my company develops and maintains an IBM i system with an RPG(LE) codebase. I was immediately intrigued and set out to learn what was happening. The problem is that learning a new paradigm of thinking is difficult.

Since I was a web developer and expressed a bit of interest in learning IBM i, I was given a user account and library that I could mess around with. I searched around various sites and some IBM documentation for a "tutorial". But, I quickly learned that there really isn't too great of a starting point compared to learning every other programming language and/or OS.

An Important Lesson

If you ever find yourself wanting to learn RPG by purchasing a used AS/400 on eBay, don't do it (unless you have an additional $20K). IBM is cool, but their software is expensive and closed source. So, I have a pretty sweet 500lb bar table in my basement now.

Brief Introduction

IBM i is an OS that works very well with business applications, reporting, data warehousing, and more. It also comes with a built in database called DB2 which uses its own little flavor of SQL.

IBM i also has the ability to use many languages such as RPG, CL, DDS, COBOL, BASIC, C/C++, Java, Python, DB2 SQL, and REXX. There is a lot to this machine, but at a high level this amount of information should be sufficient.

A big selling point of IBM i is its stability. According to developers at my workplace, our IBM i system has only needed to be rebooted once in its 30+ years of operation.

Brief History

IBM i evolved a lot over time and often gets confusing trying to google things. The easiest way to trace its evolution is to follow the RPG programming language.

  • 1959ish IBM 1400 series - RPG I
    • Punch cards and magnetic tape
    • Also supported COBOL, FORTRAN, and some ancient ASM languages.
  • 1969-1977 IBM System/3 - RPG II
    • Also supported COBOL, FORTRAN, BASIC
  • 1978 IBM System/38 - RPG III
    • Disk storage, diskette drive, etc.
    • Also supported COBOL, BASIC, PL/I
  • 1988 Application System/400 - AS/400 - RPG 400/IV
    • Also supported ASM, C/C++, COBOL, Python, REXX, and more.
  • 2000 - renamed to iSeries
  • 2006 - renamed to System i

I glossed over a lot of information, but feel free to read more.


So, wait...RPG has been around since around 1960?


RPG (Report Program Generator) started out on punch cards as a programming language that was used for generating reports. Over its life span, RPG received new features/changes and can currently be used like a general purpose programming language.

RPG fixed-format looks so ugly because of its origin. Therefore, RPG's grammar is dependent on certain columns needing specific data.

Gradually, RPG evolved out of its fixed-format ancestry and took a free-format appearance. IBM made sure that there was a decent amount of backwards compatibility between version of RPG. For example, on the AS/400 you could have a mix of RPG III and RPG IV programs. With RPG's evolution into free-format

RPG is sometimes referred to as RPGLE. Without getting into too much detail: On IBM i, there is the concept of Integrated Language Environment (ILE) languages. ILE languages can talk to other ILE languages. This includes CL, COBOL, C/C++, RPG, and more. Modern RPG development is typically using RPGLE.

Hello World in fixed-format RPG (RPG III)

      C                     MOVEL'HELLO'   HELLO  11
      C                     MOVE 'WORLD'   HELLO
      C           HELLO     DSPLY          WAIT    1
      C                     SETON                     LR
Enter fullscreen mode Exit fullscreen mode

Hello World in fixed-format RPGLE (RPG IV)

      C     'Hello World' DSPLY
      C                   SETON                                        LR
Enter fullscreen mode Exit fullscreen mode

Hello World in free-format RPGLE (RPG IV)

       dsply ('Hello World');
       *inlr = *on
Enter fullscreen mode Exit fullscreen mode

With the use of the /free and /end-free you can mix and match fixed and free RPGLE.


This is just a small glimpse at IBM i. There is a mountain of information to learn about the machine, most of which I haven't learned yet. I know this was probably confusing, but I hope my writing was coherent enough to enjoy reading. If anyone would like to read and learn more about IBM i let me know in the comments. I'd love to keep making posts like this.

Possible future posts:

  • What is Control Language (CL) ?
  • What is Data Description Specification (DDS) ?
  • IBM i file structure, Physical Files, and Logical Files
  • Calling IBM i from Java, Python, and more
  • Writing a basic RPGLE program

My IBM i "Projects"

To start learning I made a small repository to dump random files and notes into; Located at

I am writing a small "book" called "Learning IBM i as a Lowly Web Developer" (obviously the title is poking fun). This book will be a casual guide to IBM i , introductions to various obscure languages (RPGLE, CL, DDS, REXX, COBOL, etc), and a short course to wrap-up concepts.

To go along with my book, I am casually developing an IBM i VS Code extension and editor API to enable viewing, editing, and compiling IBM i code from the comfort of VS Code.

Thank you for reading.

Top comments (5)

programmersio profile image

Learn and be a part of biggest rpgle team- Our AS400 experts have extensive knowledge of ERP, EDI packages, therefore we understand each and every detail of IBM iSeries development. From providing assistance or maintenance to application development from scratch, our AS400 system development team knows it all.

worksofbarry profile image
Liam Barry

Where can we find the book when it's done? :)

barrettotte profile image
Barrett Otte

Thanks for asking! I'm still planning out a lot of it (and learning), but a basic skeleton of what I plan to do can be found here

Gitbook is a little janky sometimes with its github imports so I may use a different format at some point in the future. All of the markdown I'm using will be in this repo

I hope to keep up with writing and posting more on here as I complete the planned chapters so it doesn't fall through the cracks

sagartyagi121 profile image
Gajender Tyagi

We would love it if you keep posting about IBMi.

barrettotte profile image
Barrett Otte

Great to hear, as I find more fun stuff with IBMi I'll try my best to keep posting. Thanks !