On-disk Structure (ODS)
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Each release of InterBase has characteristic features in its internal file format. To distinguish between the file formats, InterBase records an on-disk structure (ODS) number in the database file. In general, major ODS versions (those incrementing the number to the left of the decimal point) introduce features that are not backward compatible with earlier ODS versions.
The InterBase 2020 Update 5 format is ODS 18, but still supports existing databases with ODS 17 through 13. Older ODS version are not supported and can not be connected to. It is strongly recommended to back up and restore your database so it can be upgraded to ODS 18 and benefit from the newer features.
When you create a new database or restore a backup file in the current version of InterBase, the resulting database file has the current ODS version.
To upgrade the ODS of an older database, you must back it up using the backup utility for the version of the existing database and then restore it using the current version of InterBase.