Start8 is 64 bit on a 64 bit OS in all the bits that matter. Start8_64.dll is the bit that does things.
Yes the config UI is a 32 bit process, but it doesn't need access to more than 2GB of memory. All it does is write registry keys. By sharing the same exe for both 32 and 64 bit OSes we keep the installer smaller and reduce testing requirements.
