Complex sentence: Extended Memory 64-bit Technology (EM64T) is an implementation of the AMD64 architecture, an extension to the IA-32 instruction set developed by AMD which adds 64 bit extentions to the x86 architecture.
Split into simpler sentences: Extended Memory 64-bit Technology (EM64T) is an implementation of the AMD64 architecture, an extension to the IA-32 instruction set. It was developed by AMD which adds 64 bit extentions to the x86 architecture.