the btrieve file format consists entirely of pages, which is the data that moves between memory and storage media when the engine performs an i/o operation. versions prior to 6.0 merely used data pages, index pages and a "file control record" (fcr). the file had an index for searching that linked to physical pages. beginning with version 6.0 "logical pages" started to be used, which are pages that are mapped to "physical pages" (pages at a fixed location in the file) on the disk through the use of a set of "page allocation tables" (pats).