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Re: Transitioning to 64bit, is it worth it, and how

On 8/4/07, Ron Johnson <ron.l.johnson@cox.net> wrote:
> On 08/04/07 12:53, Andrew J. Barr wrote:
> >> a) What are the pros and cons in switching to 64 bit mode?
> >>         - Is it faster?
> >
> > Yes. Unlike true 64-bit architectures like PowerPC, there is a penalty
> > for executing 32 bit code on amd64/em64t processors.
> Penalty?  Absolutely fscking not!!!!  The A64 processes 32 bit code
> at a similar speed to "regular" Athlon CPUs.

Do you have any sources for this? I remember quite distinctly seeing
on a mailing list, I think it was debian-powerpc in fact, that the
only reason that AMD64 operating systems have an all-64-bit user land
is because there is a penalty for executing 32-bit code, one which is
not present on other true 64-bit architectures. 64-bit code /does/ use
more memory, so it is advantageous to have a mixed userland if you can
afford it--e.g. only compiling applications that will benefit from
64-bit into 64-bit executables. This is what the OSes for other 64-bit
architectures do.

Perhaps the penalty is only under a 64-bit kernel...

Andrew Barr

We matter more than pounds and pence,
your economic theory makes no sense...

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