windows authentication has a concept of ACL(access control 
list). Means in a group we can give permissions/restriction 
to a perticular person in a group individually.
   Is sql authentication there no concept of ACL. Means we 
can't give permissions/restrictions individually. we can 
give permissoins to the hole group .
   in windows we can give permissions before enetering into 
the server.
    in sql we can give permissions after entering into the 
server only.