Dynamic Linked Libraries, are binary files that conatins subroutines linked together. These libraries ( DLL’s ) are loaded by Exe ( i.e Binary executable ) when they needs to use the subroutines built into the DLLs . Where as DLL’s and EXE files are practically the same , they both use the same Portable Executable format (PE) except for a single bit that indicates to treat the binary as a DLL or EXE.