The Search|Units command opens a window that displays all of the unit used in your program.
Select a specific unit and press Enter or double-click the unit to browse through all the symbols declared in the interface section of the unit.
If the selected unit is stored in TURBO.TPL or TPP.TPL, Borland's standard run-time libraries, or one of the standard units, you will not be able to view or edit the source code because these units have been compiled with symbol information turned off.
These units include: the System, Overlay, Graph, Crt, Dos, Printer, Strings, and WindDos units.
Seefor more information.