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AS400Decoded is organized into six topic guides. Each guide collects every article on its subject and tells you where to start.
New to the platform? Start with IBM i Fundamentals, then follow a learning path.
IBM i Fundamentals
What IBM i is, how libraries, objects, files, jobs, and security fit together, and how to set up your workstation.
Start with:
- What Is AS400 (IBM i)? A Complete Beginner’s Guide
- History of AS400 and IBM Power Systems
- IBM i vs Mainframe: What’s the Difference?
Open the IBM i Fundamentals Guide.
RPG Programming
RPGLE from first program to service programs: structure, data, decisions, loops, arrays, procedures, and modern fully free RPG.
Start with:
- RPGLE for Beginners: A Practical IBM i Learning Path
- What RPGLE Is and Where It Fits on IBM i
- RPGLE Source Members, Compilers, and Build Flow
Open the RPG Programming Guide.
CL Programming
Control Language for automation: commands, messages, error handling, job control, and data areas and data queues.
Start with:
- CL Programming Explained
- CL commands for RPG programmers: the system layer you cannot ignore
- CL in 2026: ILE Control Language, MONMSG Error Handling, Batch Orchestration, and Where CL Fits in a Modern IBM i Stack
Open the CL Programming Guide.
Db2 for i
SQL on IBM i: queries, MERGE, CTEs, window functions, procedures, triggers, JSON, transactions, and performance.
Start with:
Open the Db2 for i Guide.
IBM i Administration
Running IBM i in production: work management, security, journaling, backup and recovery, performance, and maintenance.
Start with:
- Operations and admin on IBM i: job queues, output queues, and keeping the system running
- IBM i System Operations with CL in 2026: Subsystem Management, Job Control, Data Queues, Output Queues, and Job Scheduling
- IBM i Subsystems and Job Descriptions Explained
Open the IBM i Administration Guide.
IBM i Modernization
Modern IBM i development: strategy, REST APIs and JSON, open source in PASE, Git and VS Code, cloud, messaging, and AI.
Start with:
- IBM i Modernization Basics
- IBM i Application Modernisation Roadmap in 2026: Strategies from API Wrapping to Full Rewrite and How to Choose
- IBM i Modernization: From Legacy AS400 Systems to Modern Enterprise Architecture
Open the IBM i Modernization Guide.
Learning Paths and Reference
- IBM i Learning Paths: guided routes for beginners, RPGLE developers, SQL developers, and administrators.
- IBM i Developer Reference: where each common command, built-in function, opcode, and SQL feature is explained.