Processor architectures

x86-64 architecture is also known as x86_64, x86-64, x64, or amd64. This refers to a family of processors based on the Intel 8086 and which are compatible with the 64-bit CPU architecture used in modern Intel and AMD processors.

x86 started out as a 16-bit instruction set for 16-bit processors, starting with the Intel 8086 launched in 1978, a 16-bit extension of Intel’s early 8-bit microprocessors. Later this was extended to a 32-bit instruction set for 32-bit processors (80386 and 80486), and more recently to a 64-bit instruction set for 64-bit processors.

It used to be written as "80x86" to reflect the changing value in the middle of the chip model numbers, but somewhere in time the 80 prefix was dropped leaving just x86, referencing only the last two digits of the early successors to the Intel 8086. Confusingly, the same family of processors is sometimes also referred to as i386 or i686, while x64 is often used as shorthand for the modern 64-bit versions, x86-64. Basically, all these terms refer to processors that use extensions of the original 8086 instruction set.