TatukGIS products use no unique internal disk format. Each supported vector file type is handled natively on disk. So opening a file of any supported format is just a matter of opening the file (using GIS.Open).
The advantage of supporting each file format natively is the software can start files more quickly and easily than if the file data had to be first converted (imported) into a TatukGIS specific format.
When a TAB, MIF, DXF, or DGN file is opened, the DK converts the file to memory-representation. Because SHP files can be mapped to memory more efficiently, SHP layers can run just a bit faster than the other supported formats.
For more about in-memory layers, refer to KB10327.