Hello Friends

I have a query related to backups and recovery operations.
I am currently operating windows Nt Server with Oracle 8i.
I have set Database in ArchiveLog Mode with automatic archival enabled.
I have set log_archive_dest_1 and 2 in 2 different drives.
Now As I see In both the directories the no. of files are
increasing which are .ARC files. in zip files format.
My query is till what time these archive files are useful
and at what time they should be deleted since my auto archive is enabled ?
Also I would like to know at what particular interval the data in the
.ARC files is commited to the database.

Thanks
Amol