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🗂️ Journey of Source to Executables(aka Load Modules in Mainframe)​

🧩 Modular Programming Concept​

As complexity increased, writing everything in a single program became impractical, leading to the introduction of modular programming.

🔖 What is Modular Programming?​

  • Modular Programming = Dividing a large program into smaller, manageable units called modules.

  • Each module performs one specific function and is written in symbolic language (COBOL/Assembler).

📋 Checklist: Why Modularize?​

  • Easier to develop, debug, and maintain.

  • Improves readability and enhances collaboration.

  • Allows reuse of modules in multiple programs.

📌 Key Reminder​

  • Write small, focused modules — each should perform one responsibility.

  • The main program controls the flow without duplicating logic.

🔥 Bonus: Real-World Thinking​

  • Reusability: Can a module be reused across different programs?

  • Maintainability: Can modules be updated without impacting the entire system?

Yes! That’s the power of modular programming.

🛠️ Compilation Process in Mainframe​

The journey from Source Code ➔ Executable Program (Load Module) involves key steps:

📑 Step 1: Compiling Source Code to Object Deck​

  • Compiler creates a pre-final Object Deck from error-free source code.

🧩 What Does an Object Deck Contain?​

  • Control Dictionaries (ESD/RLD): Resolves cross-references between modules.

  • Text Section: Contains actual program instructions and data.

  • End of Module Indicator: Marks the module's end.

🔗 Step 2: Object Deck to Final Executable (Load Module)​

  • IBM Binder links object decks into a final executable.

🛠️ How the Binder Works:​

  1. System Dependencies: The binder locates system libraries and shared resources.

  2. Object Dependencies: The binder links object decks to form the executable.

  3. Output Executable: The binder produces the final executable program.

📚 Library Terminology:​

  • Source Library: Stores source code.

  • Object Library: Contains object decks (intermediate files).

  • Load Library: Stores load modules (final executables).

🏁 Final Step: Run the Program​

Once everything is linked, execute the program using the load module.