1. Intoduction to Application Programming

1.1 What is an Application

In very simple terms, an application is just a tool or program that helps you do something. It’s like a tool in your toolbox, but instead of using it physically, you use it on a computer, phone, or tablet.

Examples:

• A calculator app helps you do math.
• A photo editing app helps you adjust or change pictures.
• A messaging app lets you send text or video messages to people.

Applications can be anything that helps you complete a task, whether it's checking the weather, playing music, or even ordering food.

So, in short, an application is just something that makes a task easier or helps you achieve something using technology

1.2 What is an Mainframe Application

A Mainframe Application is a software program or system designed to run on a mainframe computer, which is a powerful and large-scale computer used primarily by large organizations for handling high volumes of data processing and transaction management. These applications are typically built to perform mission-critical tasks such as:

• Transaction processing (e.g., banking transactions, order processing)
• Batch processing(e.g., payroll processing, report generation)
• Data management and storage (e.g., managing massive databases)
• Enterprise resource planning (ERP) (e.g., inventory control, accounting)

Mainframe applications are often built using specialized programming languages like COBOL, PL/I, and Assembler and are commonly found in industries like banking, insurance, retail, and government, where reliability and performance are critical.

1.3 Role of OS in Application Programming

1. The Operating System provides the environment in which applications run and ensures they have the resources needed.
2. The Operating System also provides developers with the tools, system calls, and APIs to interact with hardware and perform tasks easily.
3. The OS makes application development smoother and more efficient by handling many of the low-level details that would otherwise be difficult to manage.

1.4 Application programming Life cycle overview

The process of application programming in a mainframe environment involves several key steps, from planning and designing the application to coding, testing, and maintaining it.

Examples:

• The business requirements are gathered (how salaries, taxes, and bonuses should be calculated).
• System is designed and the programming language is decided based on the best availability of resources.
• Requirements are split based on logic and complexity for ease of development in codable chunks also known as modular programming.
• It's tested, approved and then deployed on the mainframe, where it processes payroll in batches or in real-time (depending on the design).
• After deployment, the system is monitored to ensure it continues to run efficiently and is updated with any necessary changes (e.g., tax rate adjustments).

1.5 What are executable and what do they mean?

An executable is a file that contains instructions your computer can run directly. When you "open" or "run" an executable file, your computer follows those instructions to perform a specific task, like opening a program, running a game, or performing calculations.

Example:

A program like Google Chrome or Microsoft Word is an executable. When you click on the Chrome icon, the operating system runs the executable file, and the browser opens.

In Simple words, Operating system needs an executable to perform the task. These executables are typically the result of converting source code written in languages like COBOL, PL/I, or Assembler into machine-readable instructions that the mainframe can execute.