The base.dcl and acad.dcl files contain the predefined tiles and DCL dialog boxes that AutoCAD uses.
These files are included with AutoCAD, and are distributed in the User Support folder. To see the path to the User Support folder, use the AutoCAD ACADPREFIX system variable.
The base.dcl file shows the DCL definitions for the basic, predefined tiles and tile types. It also contains definitions for commonly used prototypes. The PDB feature does not allow you to redefine the predefined tiles. The acad.dcl file contains the standard definitions of all the dialog boxes used by AutoCAD.