x86, amd64, ia64, EM64T

 

http://blogs.msdn.com/b/heaths/archive/2005/02/17/x86-and-ia64-and-x64-oh-my.aspx

So what is difference between x86, AMD64, IA64, and x64?

- x86 is what most everyone is running now - 32-bit processes on 32-bit Windows.

- AMD64 is Advanced Micro Devices, Inc.'s answer to 64-bit computing that runs 32-bit code natively as well. This means that you can install 32-bit Windows on an AMD64 machine. These machines have already begun shipping with 32-bit Windows XP and a friend of mine in MN is already running one happily.

- IA64 - or Intel Itanium - processors run 64-bit natively and offer 32-bit emulation, but you cannot install 32-bit Windows on it. You need to run Windows Server 2003 for 64-bit Itanium-based Systems.

- Intel has also introduced EM64T - or Extended Memory 64 Technology - for Intel Xeon processors. This processor also supports running 32-bit processes natively like the AMD64.