Boxing is used to store value types in the garbage-collected heap. Boxing is an implicit conversion of a value type to the type object or to any interface type implemented by this value type. Boxing a value type allocates an object instance on the heap and copies the value into the new object
explicit boxing is never required:
Unboxing is an explicit conversion from the type object to a value type or from an interface type to a value type that implements the interface. An unboxing operation consists of:
—Checking the object instance to make sure that it is a boxed value of the given value type.
—Copying the value from the instance into the value-type variable.
unboxing of value types to succeed at run time
int i = 123; // a value type
object o = i; // boxing
int j = (int)o; // unboxing