What is the purpose of Database Write and what it writes ?

DBWn is the background process that writes in datafiles when ever the situation arise. The situation can be
1. when a tablespace is placed in backup
2. a tablespace is taken offline to make it unavailable or changed ro Read only
3. when ever user drop segment
4. when buffers in the database buffer grows large
5. users initiated server process searched too long for buffer space when reading into buffer cache