how to detect OS architecture?

[MrSmith]

> version(Windows) {
>       // Windows code goes here
> } else {
>      // Other OS code goes here
> }
>
> More here: http://dlang.org/version.html

I think he wants determine at runtime what architecture x86 or 
x64 processor supprots and launch appropriate executable.

I think this is what he want 
http://dlang.org/phobos/core_cpuid.html#.isX86_64