The .NET Ecosystem

What is .NET?

.NET is a free, open-source, cross-platform development platform created by Microsoft. It's a complete ecosystem for building applications—from web apps and APIs to desktop software, mobile apps, cloud services, games, and IoT devices.

A Brief History: From .NET Framework to Modern .NET

.NET Framework (2002-2019)

The original .NET Framework was released in 2002 and ran only on Windows. It powered millions of enterprise applications but had limitations—it was Windows-only, monolithic, and slow to evolve.

.NET Core (2016-2020)

In 2016, Microsoft released .NET Core—a complete rewrite from scratch. It was:

• Cross-platform: Runs on Windows, macOS, and Linux
• Open-source: Community-driven development on GitHub
• Modular: Install only what you need
• High-performance: Optimized for modern workloads
• Side-by-side: Multiple versions can coexist

.NET (2020-Present)

In November 2020, Microsoft unified everything under a single name: .NET (dropping "Core"). Starting with .NET 5, the version numbers jumped to avoid confusion with .NET Framework 4.x.

Version	Release Date	Status
.NET 5	November 2020	Out of support
.NET 6 (LTS)	November 2021	Supported until Nov 2024
.NET 7	November 2022	Out of support
.NET 8 (LTS)	November 2023	Supported until Nov 2026
.NET 9	November 2024	Current (STS)

The .NET Architecture

.NET has three main components that work together to run your applications:

1. The Runtime (CLR - Common Language Runtime)

The CLR is the execution engine that runs your code. It handles:

• Just-In-Time (JIT) compilation: Converts your C# code to machine code
• Garbage collection: Automatic memory management
• Exception handling: Manages errors gracefully
• Type safety: Ensures code correctness
• Security: Enforces code access security

2. The Libraries (BCL - Base Class Library)

The BCL is a massive collection of pre-built code that handles common tasks:

• Collections: Lists, dictionaries, queues (you've used these!)
• File I/O: Reading and writing files
• Networking: HTTP clients, TCP/IP sockets
• Data access: Database connections, JSON parsing
• Security: Encryption, authentication
• Threading: Parallel processing, async/await

3. The SDK (Software Development Kit)

The SDK contains everything you need to build .NET applications:

• Compilers: Roslyn (C# compiler), F# compiler
• dotnet CLI: Command-line tools for creating, building, running apps
• MSBuild: Build system for compiling projects
• NuGet: Package manager for third-party libraries
• Templates: Project templates (console app, web API, etc.)
• Runtime: Includes the runtime for running apps

How .NET Code Executes

Understanding how your C# code becomes a running application helps you write better code.

1. You write C# code (.cs files)
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2. C# compiler (Roslyn) compiles to Intermediate Language (IL)
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3. IL is stored in assemblies (.dll or .exe files)
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4. When you run the app, the CLR loads the assembly
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5. JIT compiler converts IL to native machine code
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6. CPU executes the native code
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7. Your application runs!

Cross-Platform: Write Once, Run Anywhere

Modern .NET runs on Windows, macOS, and Linux. You can develop on any OS and deploy to any OS.

Platform	Development	Deployment
Windows	✅ Visual Studio, VS Code, Rider	✅ IIS, Windows Server, Azure
macOS	✅ VS Code, Visual Studio for Mac, Rider	✅ Docker, Kubernetes, Cloud
Linux	✅ VS Code, Rider, CLI	✅ Docker, Kubernetes, Cloud, Nginx

The .NET Family: Different Frameworks for Different Needs

.NET includes several frameworks built on top of the core platform:

ASP.NET Core (Web Applications)

The framework we'll use for InvenTrack! Build web APIs, MVC apps, Razor Pages, and real-time apps with SignalR.

Entity Framework Core (Database Access)

An Object-Relational Mapper (ORM) that lets you work with databases using C# objects instead of SQL. We'll use this extensively in InvenTrack.

Blazor (Web UI with C#)

Build interactive web UIs using C# instead of JavaScript. Runs in the browser via WebAssembly or on the server.

MAUI (Cross-Platform Mobile/Desktop)

Build native mobile and desktop apps for iOS, Android, macOS, and Windows with a single codebase.

ML.NET (Machine Learning)

Add machine learning capabilities to your .NET apps—predictions, classifications, anomaly detection.

Why .NET for InvenTrack?

Let's talk about why .NET is the perfect choice for building our mini-ERP system:

Feature	Why It Matters for InvenTrack
Performance	Handle thousands of products, customers, and orders efficiently
Scalability	Start small, grow to enterprise-scale without rewriting
Security	Built-in authentication, authorization, data protection
Productivity	Rich libraries, tooling, and IntelliSense speed up development
Type Safety	Catch errors at compile-time, not runtime
Async/Await	Handle database and API calls without blocking
Cross-Platform	Deploy to Windows, Linux, Docker, or cloud
Free & Open Source	No licensing costs, community-driven

The C# Language and .NET

While .NET supports multiple languages (C#, F#, VB.NET), C# is the primary language and the one we'll use for InvenTrack.

Key Takeaways

• .NET is a free, open-source, cross-platform development platform
• Modern .NET (5+) unified .NET Core and .NET Framework
• .NET 8 (LTS) is the recommended version for production apps
• The CLR executes your code, the BCL provides libraries
• The SDK includes everything needed for development
• C# code compiles to IL, then JIT-compiles to native code
• .NET runs on Windows, macOS, and Linux
• ASP.NET Core is the web framework we'll use for InvenTrack
• .NET offers performance, security, and productivity for enterprise apps