Fault tolerance software may be part of the OS interface, allowing the programmer to check critical data at specific points during a transaction.

Fault tolerance can include:

• Responding to a power failure (the lowest level of fault tolerance)
• Immediately using a backup system in the event of a system failure
• Allowing mirrored disks to immediately take over for a failed disk
• Multiple processors working together and comparing data and output for errors, then immediately correcting the detected errors.

In general, 100% fault tolerance can never be achieved due to cost constraints.