In transactional systems, rollback refers to

• A. Discarding uncommitted changes to a file in version control.
• B. Undoing a transaction before it is committed.
• C. Saving a transaction state to disk.
• D. Beginning a new transaction.

Answer: (B)

Rollback means undoing all the changes made by the current transaction if it hasn’t been committed yet, restoring the system to its previous state. This is essential for atomicity: a transaction should either apply all its changes or none at all. If something goes wrong, the system discards the work done so far and leaves data unchanged from before the transaction began. The other descriptions don’t match this behavior: discarding uncommitted changes in version control is not about database transactions, saving a transaction state is about persisting progress, and beginning a new transaction starts fresh rather than undoing prior work.