It seems that I was not clear enough, at least the posts of @d2010 and @440bx make me think like this.
Bitness is not the bitness of the OS, actually, in my particular case it is the bitness of data, which I get from a DLL.
In some cases, the DLL needs to store the value in an array of Word, in others it needs to store it in an array of Dword.
So what I need is to define the variable according to a parameter of the routine, in my example, it is Bitness: byte.
I will check further the links in @TRon's post,