SQL Guide : Database concepts : Transaction logging and recovery
  
Transaction logging and recovery
One of the major advantages of buying a commercial database server is that most such servers have been designed to protect data if the database server shuts down unexpectedly for any reason, such as a power failure, a hardware failure, or a failure in the database software itself.
There are a number of different ways to help protect data. We will focus on one such way, called Transaction Logging.
See also
Background
Database concepts