COBOL File Handling Basics: Sequential Files, File Status, and Practical Flow
Learn how COBOL file handling works with SELECT, FD, OPEN, READ, WRITE, CLOSE, and file status checks.
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DBala Online documents practical mainframe concepts for learners, working developers, and teams maintaining enterprise systems. Articles focus on simple explanations, examples, production-style scenarios, and safe modernization thinking.
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Latest articles
Original tutorials and notes written for mainframe learners and production-support developers.
JCL JOB, EXEC, and DD Statements Explained for Beginners
Understand the three core JCL statements used in almost every mainframe batch job: JOB, EXEC, and DD.
JCL Return Codes and Conditional Execution: How Batch Flow is Controlled
Learn how JCL return codes control step execution using COND, IF/THEN/ELSE, and production-safe patterns.
GDG Basics in JCL: Generation Data Groups Explained with Examples
Understand GDG datasets, relative generations, and common JCL usage patterns for daily batch processing.
DB2 Cursor Basics for COBOL Programs
Learn how DB2 cursors work in COBOL programs and when to use DECLARE, OPEN, FETCH, and CLOSE.
DB2 Indexes and Access Paths Explained Simply
Understand how DB2 indexes influence access paths and why EXPLAIN matters for performance tuning.
Purpose: This site is maintained by Balasubramanian Duraiswamy to share practical mainframe learning notes and modernization ideas based on enterprise development and support experience.