Question

define mixed element in short

Answer 1

To enable character data to appear between the child-elements of "letter", the mixed attribute must be set to "true". The <xs:sequence> tagmeans that the elements defined (name, orderid and shipdate) must appear in that order inside a "letter"element.
:-)

Answer 2

 1-CPU
2- Main memory
3- I/O modules
4- System bus .