Intel also has patents on many x86_64 extensions and AMD has patents on x86_64 itself. I believe MMX expired recently, so a Pentium III level CPU could be imple

Intel also has patents on many x86_64 extensions and AMD has patents on x86_64 itself. I believe MMX expired recently, so a Pentium III level CPU could be implemented without infringing on ISA patents. Hitachi still has patents on SH4 (though they expire this year). IBM has patents on POWER8. Oracle and Fujitsu have patents on SPARC. etc. Incidentally, I believe HP also owns some of the Itanium patents.