What is the difference between x86_64 amd64 and 64 bit?

This may not solve exact problem, but I'll clarify the difference between x86_64, amd64 and 64-bit.

Every micro-processor implements an instruction set (also called instruction set architecture or ISA in short).

64-bit ISA or 64-bit processor that the length of address bus is 64 bits. Intel/AMD have variable length instructions - they vary from 1byte to 15 bytes. So, instruction length does not determine what type(32/64-bit) processor it is.

x86_64 is name of specific 64-bit ISA. This instruction set was released in 1999 by AMD (Advanced Micro Devices). AMD later rebranded it to amd64.

Other 64-bit ISA different from x86_64 is IA-64 (released by Intel in 1999).

Actually... AMD64 is the real 64 bits architecture that AMD created and intel licensed it and uses it even today (just as AMD had the license to use x86 on the 32 bit CPUs). x86_64 far as i know is nothing more than a 32 bit CPU that can address the extra memory that a supposed 64 bit system need (so like a 32 bit system that recognizes and uses more than 4GB of RAM).