Like other elements in theABAP type concept, you can declare internal tables as abstract data types in programs or in the ABAP Dictionary, and then use them to define data objects. Alternatively, you can define them directly as data objects. When you create an internal table as a data object, you should ensure that only the administration entry which belongs to an internal table is declared statically. The minimum size of an internal table is 256 bytes. This is important if an internal table occurs as a component of an aggregated data object, since even empty internal tables within tables can lead to high memory usage. (In the next functional release, the size of the table header for an initial table will be reduced to 8 bytes). Unlike all other ABAP data objects, you do not have to specify the memory required for an internal table. Table rows are added to and deleted from the table dynamically at runtime by the various statements for adding and deleting records.
Internal Table Types Internal Table Objects