64 bit Support

Chromium currently isn't supported by 64-bit platforms. 64-bit support would be nice to do in the future, but there are some hurdles.
Fundamental

* Many binary-only plugins are only available as 32-bit libraries, which means the plugin processes must remain 32-bit. On Linux this is already addressed by nspluginwrapper.

Issues that can more easily be fixed
In descending order of difficulty:

* V8 generates x86 code; it needs to be taught a new architecture. Workaround could be using JSC, but that negates a large benefit of Chromium.
* The Windows Sandbox is very "hardcoded" on the OS structure and native function prototypes. It would require significant work to make 64-bit safe.
* Chromium hasn't been made 64-bit safe. Though it probably isn't too much work, it's not worth doing until the other pieces are in place. This includes making the IPC system cross 64-bit/32-bit compatible for communication with plugins.
* Changing the installer to include both 64- and 32-bit binaries.
* Perhaps other third-party libraries don't work? But most of them are open-source and already work fine on 64-bit Linux.

Source : http://dev.chromium.org/developers/design-documents/64-bit-support