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Re: Differences between amd64 and i386.

On Tue, Oct 18, 2011 at 11:50:08AM -0700, Instruisto Jose wrote:
> What are the main advantages of debian amd64 compared to i386 debian besides to address more than 4GB of memory?
> The standard Debian 6.0 kernel image of i386 has already been compiled with SMP-alternatives support.
> Are there differences in processing speed between them?

amd64 has twice as many register as i386.  This makes amd64 faster in
many cases.

amd64 uses sse for floating point math.  i386 by default uses only x87
which is awful slow.  This makes amd64 much faster in many cases.

amd64 can use more than 3.2GB ram without overhead of PAE.  This makes
amd64 a bit faster in some cases.

i386 is optimized for i486 level CPUs.  amd64 is optimized for a much
newer baseline since all amd64 capable CPUs are at least Pentium 4
level instructions.  This makes amd64 a fair bit faster in most cases.

Most other architectures that have moved to 64bit haven't really had the
same kind of improvements, and instead have usually just had pointer
size overhead going to 64bit.  Certainly this is true for powerpc,
sparc and mips as far as I know.  I don't believe Debian has distributions
for the 64bit variants of those, instead just a 64bit kernel and certain
libraries and programs where it makes sense to have 64bit memory space
are made.

Len Sorensen

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