These are files used to compile zlib under Borland C++ Builder 3. zlib.bpg is the main project group that can be loaded in the BCB IDE and loads all other *.bpr projects zlib.bpr is a project used to create a static zlib.lib library with C calling convention for functions. zlib32.bpr creates a zlib32.dll dynamic link library with Windows standard calling convention. d_zlib.bpr creates a set of .obj files with register calling convention. These files are used by zlib.pas to create a Delphi unit containing zlib. The d_zlib.lib file generated isn't useful and can be deleted. zlib.cpp, zlib32.cpp and d_zlib.cpp are used by the above projects.