IBM i and z/OS side by side
IBM i and z/OS solve similar business problems in different ways. Data sets become objects in libraries, JCL becomes CL, JES becomes subsystems and job queues, and COBOL shares the stage with RPG. Knowing the mapping lets you move between the two platforms and talk to both teams.
Concept by concept
| z/OS | IBM i | Notes |
|---|---|---|
| Data set, PDS member | Object in a library (for example a *FILE or *PGM) | Libraries do not nest; objects are typed |
| Catalog | Library list and QSYS | Objects are found through the library list |
| JCL | CL commands and CL programs | CL is also a programming language |
| JES2, initiators, job classes | Subsystems, job queues, output queues | SBMJOB puts a job on a job queue |
| 3270, ISPF, SDSF | 5250, PDM, WRKACTJOB and WRKSPLF | Both send screens a page at a time |
| Db2 for z/OS, VSAM | Db2 for i (physical and logical files, SQL tables) | The database is part of the operating system |
| RACF | Object authority and user profiles | QSECOFR is the security officer profile |
| COBOL, PL/I, Assembler | RPG, COBOL, CL, C, Java | RPG is the most common business language |
RPG
RPG began around 1960 as a report program generator and is now a full business language. Modern ILE RPG (RPG IV) is written in a free-form style that reads much like other languages, and is used with embedded SQL. ILE, the Integrated Language Environment, lets RPG, COBOL, CL and C modules be bound into one program, much as Language Environment does for z/OS languages.
Files: physical and logical
Traditionally, data is described with DDS (Data Description Specifications): a physical file holds the data, and a logical file gives another view or key order over it, like a view or index. Newer applications define SQL tables, views and indexes directly. Both are the same database underneath.
Skills that transfer
- Batch thinking: job dependencies, restarts and the critical path.
- Reading job logs and messages calmly and in order.
- COBOL and SQL, which both platforms use.
- Careful change control and respect for long-lived production systems.
Which language is the most common for business programs on IBM i? (three letters)
Show a hint
It started as a report program generator.
Show the solution
RPG.
Common mistakes
There are no data sets: look for objects in libraries.
Jobs are submitted with SBMJOB and controlled by CL; there is no JCL.
Modern free-form ILE RPG with SQL is actively used and developed.
What you will see at work
- Some organisations run both platforms: z/OS for the largest systems and IBM i for divisions or acquired businesses.
- Integration between them usually goes through MQ, APIs, file transfer or database replication.
- A mainframe COBOL developer can usually read IBM i COBOL straight away; RPG takes longer to learn.
Key terms
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