Databases can be run in one of two modes — the ARCHIVELOG mode or the NOARCHIVELOG mode. In NOARCHVIELOG mode, the redo log files are reused by the Oracle database engine without being copied to an offline location. In ARCHIVELOG mode, Oracle copies the filled online redo log files to one or more offline locations before they are reused. These redo log files, which are saved offline, are called archived redo log files. The ARCH process is responsible for archiving when automatic archiving is enabled. You use the archived redo log files to recover a database and update a standby database.
The ARCHIVELOG mode is very important for mission-critical production databases. Databases can be backed up in the open mode when running in the ARCHIVELOG mode. Also, the ARCHIVELOG mode provides point-in-time recovery. It is generally not necessary for test and development databases.