Introduction
The IBM AS400 (now rebranded as IBM iSeries or IBM Power Systems) has been a cornerstone of enterprise computing for over three decades. Known for its reliability, security, and robust performance, the AS400 platform continues to power critical business applications across industries such as banking, healthcare, manufacturing, and logistics. However, as technology evolves, organizations face a pivotal decision: should they continue developing applications on the AS400 platform, or should they migrate to a more modern infrastructure?
This comprehensive guide explores the pros and cons of AS400 application development versus migration, helping businesses make an informed decision based on cost, scalability, security, and long-term IT strategy. By the end of this blog, you’ll have a clear understanding of which approach aligns best with your business needs.
Understanding AS400 (IBM iSeries)
What is AS400?
The IBM AS400, launched in 1988, is a midrange server designed for business applications. It runs on the IBM i operating system, which integrates database management, security, and application deployment into a single system. The platform supports programming languages such as RPG (Report Program Generator), COBOL, Java, PHP, and Python, making it versatile for enterprise applications.
Why is AS400 Still Relevant Today?
Despite being introduced over 30 years ago, the AS400 remains a preferred choice for many organizations due to:
Unmatched Stability: The system is renowned for its near-zero downtime, making it ideal for mission-critical operations.
Built-in Security: IBM i includes advanced security features like object-level permissions and encryption, reducing vulnerabilities.
Legacy Application Support: Many businesses still rely on RPG and COBOL-based applications that run efficiently on AS400.
Scalability: The platform can handle increasing workloads without significant performance degradation.
However, with the rise of cloud computing, AI, and modern ERP systems, companies must evaluate whether to continue investing in AS400 development or transition to newer technologies.
Benefits of Developing New Applications on AS400
Cost-Effective for Existing Users
Companies already using AS400 can avoid the high costs of migration by extending their current infrastructure.
Licensing fees for IBM i are often lower than cloud-based alternatives when considering long-term usage.
Seamless Integration with Legacy Systems
Businesses with decades of data stored in DB2 can leverage existing databases without complex data migration.
RPG and COBOL applications can be modernized rather than completely rewritten.
High Security & Compliance
Industries like banking and healthcare benefit from IBM i’s compliance with HIPAA, PCI-DSS, and GDPR.
The platform’s object-based security model minimizes unauthorized access risks.
Reliable Performance for Transactional Workloads
AS400 is optimized for high-volume transaction processing, making it ideal for financial and inventory systems.
Challenges in AS400 Development
Shortage of Skilled Developers
Finding programmers proficient in RPG and COBOL is becoming increasingly difficult.
Younger developers prefer modern languages like Python, Java, and JavaScript.
Outdated User Interfaces
Traditional "green-screen" interfaces are less intuitive compared to modern web and mobile apps.
Upgrading to GUI-based applications requires additional development effort.
Limited Cloud-Native Capabilities
While IBM supports cloud deployments, AS400 was not originally designed for cloud-native architectures.
Integrating with modern DevOps and CI/CD pipelines can be challenging.
Modern Approaches to AS400 Development
To overcome these challenges, businesses can adopt:
RPG Modernization: Using tools like Rational Developer for i (RDi) to write cleaner, modular RPG code.
Open-Source Integration: Running PHP, Python, Node.js, and Java on IBM i to attract new developers.
Web & Mobile Enablement: Using frameworks like Profound.js or Laravel to build responsive front-ends while retaining the AS400 backend.
AS400 Migration: Is It the Right Move?
What Does AS400 Migration Involve?
Migration from AS400 typically means:
Rehosting (Lift & Shift) → Moving applications to cloud VMs (AWS, Azure, IBM Cloud).
*Replatforming *→ Adapting applications to run on modern databases (PostgreSQL, SQL Server).
Full Rewrite → Rebuilding applications using modern languages (.NET, Java, React).
Reasons to Migrate from AS400
Future-Proofing IT Infrastructure
Cloud-native applications offer better scalability, AI integration, and IoT compatibility.
Modern ERP systems (SAP, Oracle, Microsoft Dynamics) provide advanced analytics and automation.
Improved User Experience
Web and mobile interfaces enhance usability compared to legacy green screens.
Customers and employees expect intuitive, real-time applications.
Access to a Larger Talent Pool
Finding Java, .NET, or cloud developers is easier than hiring RPG specialists.
Cost Efficiency in the Long Run
Cloud platforms reduce hardware maintenance costs with pay-as-you-go models.
Challenges in AS400 Migration
High Initial Costs
Data migration, application refactoring, and staff training require significant investment.
Business Disruption Risks
A poorly planned migration can lead to downtime and data loss.
Compatibility Issues
Legacy RPG/COBOL logic may not translate smoothly to modern architectures.
When to Choose AS400 Development?
✔ Your business relies on stable, mission-critical AS400 apps.
✔ Budget constraints prevent a large-scale migration.
✔ Compliance requirements (e.g., banking regulations) favor IBM i’s security.
When to Migrate from AS400?
✔ Legacy systems hinder digital transformation.
✔ Employees struggle with outdated interfaces.
✔ You need cloud scalability and AI integration.
Hybrid Approach: Modernizing Without Full Migration
Instead of a complete overhaul, businesses can:
✅ Integrate APIs – Connect AS400 with cloud services like AWS or Azure.
✅ Adopt Microservices – Break monolithic RPG apps into scalable components.
✅ Modernize the UI – Use React or Angular for front-end while keeping AS400 as the backend.
Example: A logistics company keeps its IBM i-based inventory system but integrates it with a real-time tracking mobile app.
Case Studies: Real-World Examples
Case 1: Manufacturing Firm Stays on AS400
Challenge: Needed real-time analytics without disrupting operations.
Solution: Developed a Node.js dashboard pulling data from DB2.
Result: Improved decision-making without migration costs.
Case 2: Bank Migrates Core Banking to Azure
Challenge: Outdated green screens led to poor customer experience.
Solution: Migrated to Azure with .NET Core and SQL Server.
Result: Faster transactions and higher customer satisfaction.
Conclusion
The decision between continuing AS400 application development or migrating to a modern platform is not one-size-fits-all—it requires a careful evaluation of your organization’s unique needs, budget, and long-term IT strategy. For businesses that rely on stable, mission-critical applications with stringent compliance requirements, modernizing existing AS400 systems through incremental upgrades, API integrations, and UI enhancements may be the most cost-effective and low-risk approach. This allows companies to retain the platform’s legendary reliability and security while gradually adopting newer technologies. On the other hand, organizations facing scalability limitations, outdated user interfaces, or a shortage of RPG/COBOL expertise may find that migration to cloud-based or modern ERP systems unlocks greater agility, innovation, and access to a broader talent pool. A hybrid approach—where core legacy systems remain on AS400 while select functions migrate—can also provide a balanced solution. Ultimately, the right choice depends on your business goals: if maintaining operational continuity is paramount, development and modernization may be the answer, but if future growth demands cloud scalability and cutting-edge capabilities, migration could be the better investment. Consulting with AS400 specialists and conducting a thorough cost-benefit analysis will ensure you make an informed decision that aligns with your company’s vision for the future.