Free blocks have a header, but no data is stored in the blocks. These blocks can become any other valid block type. These blocks are below the high-water mark. The high-water mark is a pointer to the last formatted block within the database storage area. Free blocks can be created by extending the high-water mark of the database, extending the database, or reformatting blocks during an index rebuild. If the user deletes many records, the RM blocks are put on the RM Chain. However, index blocks can only be reclaimed through an index rebuild or an index compress.