Exchange Database file (.edb):
The .edb or the exchange database file is the repository that stores all the mailboxes of your configured mail accounts. It stores data in a B-tree structure and is directly accessed by the Extensible Storage Engine (ESE).
Streaming Media file (.stm):
The .stm file is meant to store the streamed Internet content. The file is always used in conjunction with the .edb file and collectively creates the exchange server database. Any operation on the .edb file automatically includes the .stm file and thus these files are treated as a single entity. On installation of a new Exchange Server, the priv1.stm database file is created and stores streaming Internet files.
Transaction Log file (.log):
The .log file of Exchange Server acts as a repository to store various database related operations, including creation and modification of messages. All complete as well as incomplete Exchange Server transactions are logged in these log files. These files are very helpful in Exchange disaster recovery.
Checkpoint file (.chk):
The .chk file stores the information indicating the successful saving of data to the Exchange database. This helps the ESE in recovering the database from a bad service interruption. These .chk files are saved at the same location as that of the .log files.