Runtime

A runtime (or runtime environment) is the software layer that provides everything your program needs while it is executing.

It includes:

• Code execution
• Memory management
• Threading
• Exception handling
• Type checking
• I/O access

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🔸 Why is it called “runtime”?

Because it operates at runtime — i.e., when your program is actually running (not during compilation).

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🔹 Examples of Runtimes

Language	Runtime
Java	JVM (Java Virtual Machine)
Python	Python Interpreter + VM
JavaScript	V8 Engine (in Node.js)
C#	.NET CLR (Common Language Runtime)

These runtimes execute your code and provide language-specific features (GC, safety, etc.).

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🔸 What a Runtime Usually Includes:

Feature	Purpose
Execution engine	Runs your code (e.g., bytecode interpreter or JIT)
Memory manager	Allocates heap/stack, runs GC
Thread scheduler	Manages concurrency and thread safety
Exception handler	Deals with runtime errors
Type system	Enforces language typing rules at runtime
Standard library access	Gives access to file system, network, etc.

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🧠 Example (Java):

When you run:

java HelloWorld

You’re starting the Java runtime, which:

1. Loads the bytecode (HelloWorld.class)

2. Verifies it

3. Executes it inside the JVM

4. Manages memory, threads, exceptions, etc.

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✅ TL;DR:

A runtime is the execution layer that provides the services and environment your program needs while it’s running — like memory, threads, I/O, and error handling.

Want to go deeper into JVM as a runtime, or contrast compiled vs interpreted runtimes next?