Re: 32 bit processors / 64 bit processors

[益牙 <simonyanix@gmail.com>]

On Oct 21, 2009, at 1:39 PM, 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 !

I had an understanding of this being how many bits you have to address  
your RAM.

>
>
> 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

Just did a comparison test but it tells me otherwise. But I'm not sure  
if the test case if correct, can someone improve it?
On a 64bit CentOS:
[root@yyan ~]# more test.c
#include <stdio.h>

int main ()
{
     printf ("%d\n", sizeof(int));
     return 0;
}
[root@yyan ~]# gcc test.c
[root@yyan ~]# ./a.out
4
[root@yyan ~]# uname -a
Linux yyan.pmlab.com 2.6.18-128.el5 #1 SMP Wed Jan 21 10:41:14 EST  
2009 x86_64 x86_64 x86_64 GNU/Linux
[root@yyan ~]#

On my Leopard: (Hopefully it's a 32bit OS as it shows)
simonmac:coding yansimon$ cat test.c
#include <stdio.h>

int main ()
{
     printf ("%d\n", sizeof(int));
     return 0;
}
simonmac:coding yansimon$ gcc test.c
simonmac:coding yansimon$ ./a.out
4
simonmac:coding yansimon$ uname -a
Darwin simonmac.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15  
16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386
simonmac:coding yansimon$


>
> 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?
>
>
> Please correct me if i am wrong !
> TIA,
>
> Rick
>
> --
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>
>
>
>
> -- 
> Regards,
> ~Sid~
> I have never met a man so ignorant that i couldn't learn something  
> from him
>

--
益牙

http://www.google.com/profiles/simonyanix

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