Re: 32 bit processors / 64 bit processors

[askb <askb23@gmail.com>]

On Wed, 2009-10-21 at 11:09 +0530, Siddu wrote:
> 
> 
> On Wed, Oct 21, 2009 at 8:32 AM, Rick Brown <rick.brown.3@gmail.com>
> wrote:
>         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?
>         
> 
> When they say its 32/64 bit machine its the capability of the system
> or processor to process so many bits at once !

Additionally, the virtual memory address is 64 bit. Also the main
difference is with sizeof(long int) and sizeof(void *) on both archs. 

> 
>  
> 
>         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?
>         
> its dependent on 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.
> 
> No ... 32 bit OS can run anything <= 32 bit
>  
>         A 64 bit processor may run a 32 or a 64 bit OS.
> 
> yes thats right !
>  
> 
>         A 32 bit
>         compiler genrates code only to be run on a 32 bit OS; ditto
>         for 64
>         bit. 
> 
> Not sure about this let others have their say ! 
> 
>         Is this right?

It is possible to use the -m32 and -m64 flags with gcc for generating
32/64 bit compatible code.



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