This field must be equal or greater than the total size, in bytes, of the members of the class or structure. This field is primarily for compiler writers who want to extend the memory occupied by a structure for direct, unmanaged access. For example, you can use this field when working with unions that are not represented in metadata directly.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0