By Chris Isayan, Associate VP, Digital Experience
The AS/400 system and RPG programs have been the backbone of many enterprises for decades. These applications are known for their reliability, security, and stability—so much so that many organizations cannot even recall the last time they restarted their AS/400 systems.
If these applications are so dependable, why modernize?
The primary reason is the shrinking AS/400 RPG talent pool. As experienced developers retire, it becomes increasingly difficult to maintain or upgrade these systems.
Other motivations include:
- High cost and complexity of changes due to the system’s monolithic design
- Limited integration with modern tools and frameworks
- User dissatisfaction with outdated “green screens” and limited UI capabilities
While modernization is essential, the timing and approach depend on each organization’s unique goals, risk tolerance, and long-term strategy.
Key Concerns in AS/400 Modernization
Many clients express concern about the potential loss of business logic during modernization. Over years of development, AS/400 programs have accumulated complex business rules and workflows deeply embedded in RPG code—with limited separation between screen and backend logic.
Another concern lies in the database model. AS/400 systems use a hierarchical data structure, which can be challenging for teams familiar with relational database models (RDBMS).
Modernization Challenges Include:
- Understanding legacy business rules and logic
- Transitioning from hierarchical to relational models
- Managing data migration and dependency refactoring
- Maintaining reporting integrity and backend performance
A deep understanding of these systems is crucial before modernizing the front end.
Modernization Approach: Where to Begin
Modernization usually starts with a discovery and assessment workshop. Each AS/400 system is highly customized to business operations, often with unique, one-off scenarios.
Our Process Includes:
- Identifying pain points, workflows, and business nuances
- Rationalizing existing systems — what stays, what gets rewritten, and what’s replaced
- Establishing priorities, timelines, and budgets
- Implementing modernization through reverse engineering, development, and testing
While automation tools exist for converting AS/400 front-end code, most are proprietary and unavailable for licensing.
Leveraging GenAI for AS/400 Modernization
At Prolifics, we are exploring how Generative AI (GenAI) can streamline the modernization journey.
We’ve broken the process into three essential steps:
- Understanding the legacy code
- Reverse engineering business capabilities
- Translating code into modern languages
This structured, AI-driven approach helps accelerate transformation while maintaining code quality and business logic integrity.
Practical Application Example
- Point the AI to a supply chain ERP codebase
- Ask it to describe the procurement workflow
- Generate code for a “New Purchase Order” screen using Angular (front-end) and Node.js (middle-tier)
By creating a scaffold code with architectural decisions, design patterns, and best practices, GenAI-generated code can be efficiently integrated—balancing automation with manual control.
Overcoming GenAI Challenges
While GenAI adds value, there are important considerations:
1. Outdated Training Data
Models like ChatGPT may rely on outdated frameworks. To address this, we provisioned a custom LLM on the cloud, fine-tuned for current libraries and best practices.
2. Inconsistent Code Outputs
Each generation can vary slightly. To achieve consistency, we use:
- Temperature control parameters
- Predefined templates
- Manual code review and unit testing
Even with these precautions, manual validation remains essential for production readiness.
It’s worth noting that IBM watsonx Code Assistant for Z follows a similar hybrid approach, combining rules-based translation with GenAI—although it currently supports only Mainframe COBOL on Z systems.
Coexistence of Legacy and Modern Applications
Modernization doesn’t happen overnight. Many organizations must run legacy and modern systems simultaneously during transition phases.
Best Practices for Coexistence:
- Roll out modernization in phases (e.g., procurement → inventory → logistics)
- Develop a legacy decommissioning plan
- Optimize hardware and resource utilization for both environments
- Train existing staff to manage modern applications
Proper planning minimizes operational disruption and ensures continuity throughout the transformation journey.
Deployment & Change Management
End-user adoption can make or break modernization success. Many long-time AS/400 users love their keyboard-driven green screens for speed and familiarity.
Key Success Factors:
- Maintain critical functionality during modernization
- Deliver complete business workflows to avoid switching between systems
- Enable single sign-on (SSO) for seamless navigation
Change Management Essentials:
- Keep a log of user concerns and changes
- Develop comprehensive Run Books
- Communicate updates transparently
- Provide pilot user programs to champion adoption
The goal is zero disruption and maximum efficiency in daily operations.
Conclusion
More organizations are now transitioning from AS/400 RPG to modern programming environments. The key is to start while RPG expertise is still available in-house, ensuring continuity and smoother knowledge transfer.
Partnering with experienced digital engineering experts ensures:
- Accurate code reverse-engineering
- Automated quality assurance
- Effective training and knowledge handover
At Prolifics, we combine GenAI-driven prototypes, accelerators, and automation testing tools to fast-track modernization with quality and precision. Our integrated approach empowers your teams to take ownership and maintain the new systems confidently post-transition.
Special Thanks
Special appreciation to Konrad Konarski, Gregory Hodgkinson, Honda Bhyat, Rajeev Sharma, Ramnath Nalluri, and Sheryl Oleksa for their insightful contributions to this blog.
About the Author
Chris Isayan, Associate VP, Digital Experience at Prolifics, specializes in global-scale digital transformation and modern application design. Known for his “learn the industry first” approach, Chris leverages Cloud, AI/ML, NLP, and computer vision technologies to accelerate enterprise innovation.