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.DCU File Extension

File Type	Delphi Compiled Unit
File Format	File
Common?	No
File Description	Compiled unit (.PAS) file; typically has the same name as the source code file, i.e. "source.dcu" is the compiled version of "source.pas"
Program(s) that open dcu files	Windows: Borland Delphi

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/dcu