For more information on transactions, see Chapter 17 in the Transact-SQL User's Guide. Logs The SQL Server uses a log to keep track of all transactions. Each database has its own log. The log is part of the database and is not human readable. Each change made to a database is saved in the database's transaction log.
Some databases save their data and log information in the same area.
Most databases have separate areas for the data and their log. Each area of a database is called a segment. You can create a database where all three segments are on the same device. If you do this, you won't have as much control over the database as you'd like. The best way to create a database is to separate the log segment from the system and default segments.