When the user creates the environment variable in a set operation, the operating system stores the environment variable in the system registry, but not in the current process. If the user starts a new process, the operating system copies the environment variable from the registry to that process.

When the process terminates, the operating system destroys the environment variable in that process. However, the environment variable in the registry persists until the user removes it programmatically or by means of an operating system tool.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 2.0.0.0, 4.0.0.0
Since: .NET 2.0