The Common Language Runtime (CLR) is an environment that manages code execution and provides application-development services. Compilers such as VB .NET expose the CLR’s functionality to enable developers to create applications. Code that is created under this environment is called managed code . Note that COM components are not managed code, although they (as well as other unmanaged code) can be used in applications that are built under the CLR.
The output of a compiler includes metadata , which is information that describes the objects that are part of an application, such as:
Data types and their dependencies
Objects and their members
References to required components
Information (including versioning information) about components and resources that were used to build the application
Metadata is used by the CLR to do such things as:
Manage memory allocations
Locate and load class instances
Manage object references and perform garbage collection
Resolve method invocations
Generate native code
Make sure that the application has the correct versions of necessary components and resources
Enforce security
The metadata in a compiled software component makes the component self-describing. This implies that components, even those written in another language, can interact with the given component directly.
Objects that are managed by the CLR are referred to as managed data. (It is also possible to use unmanaged data in applications.)
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