C# 9.0 in a Nutshell

Chapter 5. .NET Overview

Almost all of the capabilities of the .NET 5 runtime are exposed via a vast set of managed types. These types are organized into hierarchical namespaces and packaged into a set of assemblies.

Some of the .NET types are used directly by the CLR and are essential for the managed hosting environment. These types reside in an assembly called System.Private.CoreLib.dll and include C#’s built-in types as well as the basic collection classes, and types for stream processing, serialization, reflection, threading, and native interoperability.

Note

System.Private.CoreLib.dll replaces .NET Framework’s mscorlib.dll. Many places in the official documentation still refer to mscorlib.

At a level above this are additional types that “flesh out” the CLR-level functionality, providing features such as XML, JSON, networking, and Language-Integrated Query. These comprise the Base Class Library (BCL). Sitting above this are application layers, which provide APIs for developing particular kinds of applications such as web or rich client.

In this chapter, we provide the following:

• An overview of the BCL (which we cover in the rest of the book)

• A high-level summary of the application layers

What’s New in .NET 5

.NET 5 features numerous performance improvements over .NET Core 3, including to the garbage collector, Just-In-Time (JIT) compiler, regular expressions processor, HTTP processor, LINQ, collections, and more.

.NET 5 also includes the runtime support for C# 9’s ...