Answer:
file system is based on ISAM. It takes time to search a data in a file (table). It is very difficult to maintain physical refrential integrity. It's not an easy talk to patition or scale out a database.
RDBMS is quite wide concept. Everything is under one logical box. We can maitain data integrity, reduce the redundancy and increase the consistency of the data. It is very easy to maintain the data and scale out it.