Hi, Firstly, I'm trying to understand what exactly characterizes a procesor or an operating system as 32bit / 64 bit. I've read that it means the "native word size" of a machine. But what exactly is that? Register size? Address bus size? Anything else? Secondly, I'm trying to understand what exactly does a sizeof(int) depend on when we say it is "platform specific". Is it dependent of compiler being 32bit / 64 bit? Or the OS being 32bit / 64 bit? Or the processor being 32 / 64 bit? Lastly, How are "sizes" of compiler / OS / processor inter related? Here is my understanding. A 32 bit processor can only be running a 32 bit OS. A 64 bit processor may run a 32 or a 64 bit OS. A 32 bit compiler genrates code only to be run on a 32 bit OS; ditto for 64 bit. Is this right? TIA, Rick -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs