Actual benefits of amd64 over i386

David O'Brien obrien at
Wed May 18 22:46:36 PDT 2005

On Fri, May 13, 2005 at 04:17:11PM -0300, Joo Carlos Mendes Lus wrote:
>     What about a 64 bit kernel, and mixed mode (32bit and 64bit)
> userland?  Solaris does this, and it sounds efficient, from the comments
> I've seen in this list.

When Sparc went from 32-bits to 64-bits the calling ABI was not changed.
Nor were the number of registers increased.  So it is w/o a doubt that a
32-bit Sparc binary runs faster than a 64-bit one (abit 64-bit math and
large memory).  This is not true of AMD64 - the number of registers was
doubled and the calling ABI changed and optimized.

>     The bad part: Most (probably all) libraries would duplicated, and
> the kernel and compiler should be modified to understand this "feature".

We already duplicate all the shared libraries.

>     If amd64 32bit executables were compatible with (maybe the same)
> i386 executables, even better.  Note that I am not talking about i386
> emulation.  I am talking about native 32 bit executables in amd64 arch.

What is the difference of "i386 emulation" and "native 32 bit executables
in amd64 arch"??

-- David  (obrien at

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