I86

i86 is a family of microprocessors from Intel, generally taken to be all microprocessors that derive from the 8086 or are compatible with that processors instruction set, although the architecture and the origins of the instruction set can be traced all the way back to the 4004 processor that was designed by Intel and Busicom.

x86
x86 is taken to mean all i86 microprocessors from Intel and all compatible processors from other manufacturers such as AMD, VIA and DMP.

AMD64
Sometimes called x64, a 64 bit CPU architecture developed by AMD that shares some architectural similarities with the i86 family, has a strong similarity with its instruction set and can execute 32-bit i86 code as well as its native instruction set.