Green Screens: Why Enterprise Engineers Still Demand…
Hi all,
This article is all about AS400 systems, which I saw in a job description at an enterprise company. They required both legacy and modern tech stacks, like AS400, RPG, DB2, and modern software stacks.
So I did R&D stuff for this fintech company’s job descriptions. I also knew about these legacy systems, but these old systems are not legacy systems according to a book called “Working Effectively with Legacy Code” by Michael C Feathers. A legacy system is a system without proper tests.
I’m not against agentic AI or vibe coding developments. But I’m also interested in maintaining legacy systems. I crawled YouTube and LLMs to find those systems; they are old-fashioned but have complete documentation.
There are so many documents online with huge user manuals. I use an LLM to summarise them and configure the AS400 system using a simulator software called MochaSoftTN5250.Those technologies are still used worldwide in enterprises domains like Fintech, insurance,foods and supply chains even governments arround world,even SriLanka and USA. They are still being managed and are struggling with maintenance. It is highly secure and has high uptime according to data, and it is also not vulnerable to cybersecurity attacks.
- Everything is an Object (OBJ): In IBM i, files, compiled programs, user profiles, and queues are all treated as structured objects. Every object has a type—such as PGM(Program), FILE(File), or LIB(Library).
- Libraries (LIB): Instead of nested directories (e.g., /user/bin/heshan), IBM i uses flat containers called Libraries. A library cannot contain another library; it holds objects directly.
- Source Physical Files (FILE): Unlike standard OS files, source code on IBM i is stored inside special tables called Source Physical Files (e.g.,
QCBLSRCfor COBOL). - Source Members (MBR): Inside a Source Physical File, individual programs exist as Members.
IBM has its own environments like,
- IFS,
- Data Queues,
- Object-Level Security & Authorisation Lists,
- Built-In Backup & Recovery,
- DB2 databases.
Of the above points, I know only DB2; it is an SQL database for these systems so far, and all are included with this system.
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I’m a noob in this stack, and enterprises need experienced developers/maintainers for maintaining critical systems. But in the world, previous maintainer leads or seniors are retiring, but there is no next batch of people who can maintain systems; that is the bottleneck, and it is a huge problem for company owners. Some are integrated coding agents like IBM BOB to mitigate this issue.
There are so many other challenges related to IBM I systems, such as,
- IBM i is deeply tied to proprietary hardware (IBM POWER systems) and closed-source operating microcode (SLIC/TIMI).
- Traditional IBM i development relied heavily on direct green-screen editing (SEU/PDM) and library-based object locking, rather than modern distributed source control.
- To developers trained purely in modern web stacks (Node.js, React, Python), the classic 5250 green screen looks ancient and intimidating.
- The operating model of IBM i — featuring Single-Level Storage, object-based security, libraries instead of directories, and library lists *LIBS—is completely different from Linux or Windows.
I tried to log in to an AS400 system; you don't need to have physical access to learn it. You can easily create an account in IBM Cloud, and they give a default username and password.
And modern IDEs like VS Code have an extension called IBM I and you can easily login by username and password you created at IBM.
I think this content is enough for this article, and I’m still curious and learning how this system works and its abilities for enterprises worldwide. Companies need seasoned developers who have deep knowledge of concepts with practicals. This is just the beginning of it.
Thanks for reading!. Stay curious, stay learning!!!
