Difference Between Hashtable and Dictionary

1. Hashtable is threadsafe and while Dictionary is not.
2. Dictionary is types means that the values need not to boxing while Hashtable 
    values  need to be boxed or unboxed because it stored the  values and keys as 
    objects.         
3. When you try to get the value of key which does not exists in the collection, the 
    dictionary throws an exception of 'KeyNotFoundException' while hashtable returns 
    null value.
4. When using large collection of key value pairs hashtable would be considered more 
    efficient than dictionary.
5. When we retrieve the record in collection the hashtable does not maintain the order 
    of entries while dictionary maintains the order of entries by which entries were added.
6. Dictionary relies on chaining whereas Hashtable relies on rehashing.