# Fundamentals

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## .NET Components

### Common Language Runtime (CLR)

#### Common Type System (CTS)

The *common type system* defines how types are declared, used, and managed in the common language runtime, and is also an important part of the runtime's support for cross-language integration.

It is designed as a singly rooted object hierarchy with `System.Object` as the base type from which all other types are derived.&#x20;

All types in .NET are either ***value*** types or ***reference*** types.

* ***Value Types:*** Contain the values that need to be stored directly on the stack or allocated inline in a structure. They can be built-in (standard primitive types), user-defined (defined in source code) or enumerations (sets of enumerated values that are represented by labels but stored as a numeric type).

> **Value** types are data types whose objects are represented by the object's actual value. If an instance of a value type is assigned to a variable, that variable is given a fresh copy of the value.

* ***Reference Types:*** Store a reference to the value‘s memory address and are allocated on the heap. Reference types can be any of the pointer types, interface types, or self-describing types (arrays and class types such as user-defined classes, boxed value types, and delegates).

> **Reference** types are data types whose objects are represented by a reference (similar to a pointer) to the object's actual value. If a reference type is assigned to a variable, that variable references (points to) the original value. No copy is made.

#### Common Language Specification (CLS)

The *common language specification* defines a set of features that are needed by many common applications.

CLS is a subset of the CTS. This means that all of the rules in the CTS also apply to the CLS, unless the CLS rules are more strict.

#### Framework Class Libraries (FCL)

### Base Class Libraries (BCL)

{% embed url="<https://endjin.com/blog/2022/07/understanding-the-stack-and-heap-in-csharp-dotnet>" %}


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