Archived redologs are one of the most important distinguishing feature of Oracle. They are the most basic component and an essential part of any production and self-respecting database.

They are used everywhere. From media recovery to log miner, and from standby database to golden gate.

What exactly do they contain?

They store, redo records, composed of change vectors describing changes made to database blocks. Each change vector describes a single transactional change to a database block. Each change vector is marked by a unique number called as System Change Number (SCN). Change vectors also are stored for changes to the rollback segment data blocks and the transaction table of the rollback segments.