What is the difference between master detail and many to many relationship in Salesforce?

Master-detail relationship

1)in master-detail relationship field value is mandatory
2) here parent record is deleted automatically child records is deleted
3) an object is allowed only 2 master-detail relationship fields
4) if we give any rules to parent that rules automatically goes to the child. Child does not contain any separate rules.
5)we can directly convert master-detail relationship to lookup relationship
6) if we give a value to master-detail relationship field that value does not change.

Lookup relationship

1)in lookup relationship field value is not mandatory
2) here parent record is deleted automatically child records are not deleted
3) an object is allowed only 25  relationship fields
4) here parent rules and child rules are maybe same or not.
5)if we cannot give a value to the lookup field then we can't directly convert lookup relationship to master-detail relationship here first we need to give a value to the lookup field.
6) if we give a value to lookup relationship field we can change that value whenever we required.