RE: 64-bit Linux On 32-bit processors

On Thu, 12 Aug 2004, Upendra Adarkar wrote:

> Dear Friends
>
> I don't see any problem running 64bit OS on 32bit system. I am able to
> install solaris 8 (64bit) on ss20 (32bit sparc processor).

You are mistaken. When you install Solaris 8, you get two sets of 
kernels/librairies. You selected 64bit support during install but if you 
verify what your system is really running, then you will see that you are 
only running the 32bit kernel and the 32bit libraries. (use 'isainfo -v' 
to see this). Try running a SPARCV9 (64bit) binary on your ss20 and it 
will fail.

> Please note: when you install 64bit os on 32 bit processor. The
> performance and environment what you get is 32 bit only.

You cannot run a 64bit OS (kernel + libs) on today's 32bit processors. 
Period. Even then, most 64bit processors allow 32bit code to execute 
because some 'compatibility' layers were included but the reverse just has 
not been designed (who would need a 32bit processor able to understand and 
execute 64bit assembly? People usually design a 64bit processor and allow 
for 32bit code to execute).

> If you develop application on (32bit processor 64 bit OS) environment
> you may need to recompile once again on entire 64bit environment then
> only you will get desire results.
>
> On Sun Sparc (solaris) environment you can run all your 32bit
> applications on 64bit environment without compiling. But you may not get
> desire optimum performance.

That's because SUN provides two sets of libraries: 32bit libraries 
(/usr/lib) and 64bit libraries (/usr/lib/sparcv9). 32bit apps will 
transparently use the 32bit libraries whereas 64bit apps will use their 
64bit counterparts. Performance is a different matter: 64bit code is 
slower than 32bit code but your 64bit processor might (will?) be able to 
circumvent this drawback because it was optimized for 64bit.

Cheers,

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