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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] Enabled building of x86_64 code on Mac OS X
Date: Tue, 27 Jan 2009 00:34:03 +0000
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To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>

> Out of curiousity, what are the benefits of using 64-bit apps in OS X?

My guess is that same as most other x86 targets: The i386 legacy mode is 
crippled by lack of registers, modern x86 hardware has a big fat wide memory 
bus, and noone's bothered implementing an ILP32 64-bit API[1], so 64-bit apps 
give measurably better overall performance.

Paul

[1] ILP32 APIs for 64-bit x86 do exist, but the architecture is missing a 
couple of features so they're a bit hairy, and AFAIK not supported by any 
mainstream operating systems.