why control class has SynchronizationContext ?

Hi,

I am looking multithread part , I heard few buzz words say SynchronizationContext, ExecutionContext and CallContext. what this class ?

Can any one tell me what this all and why control class only can create SynchronizationContext ? and what else context classes are there ?

Note: If some one gives me a diagram structure of a exe(Process) could be appreciatable .Let say first os , next process then .net BCL then AppDomain etc...