unmanaged code is not varify by clr,and clr is not varify 
third party control and pointer.

Unmanaged code use like using dll or any other com object 
in application then it is unmanaged code ,we cannot change 
the code.

Using 
unsafe
{ 
//unmanaged code;
}

All the components that are developed using the languages 
that are not supported by the CLS are called unmanaged code 
that means which is not viable to run under the CLR. All 
the COM components are unmanaged and all the ASSEMBLIES are 
managed. We can even run the unmanged code components in 
the CLR using ComCallableWrapper class.