In general, DWORD is unsigned long. While any 32-bit compiler treats this type as 32 bits wide, 64-bit compilers treat this type differently. With Windows 64-bit compilers the size of this type is still 32 bits. However, with UNIX 64-bit compilers (e.g. GCC, SUN Forte) the size of this type is 64 bits. In order to avoid compiler dependency issues, use the UINT32 and UINT64 cross-platform types when you want to refer to a 32-bit or 64-bit address, respectively.