X86

x86 is a term used to describe a CPU instruction set compatible with the Intel 8086 and its successors, including the Pentium and others made by Intel and other companies. This is the CPU architecture used in most desktop and laptop computers. Many 21st century workstations and servers also use x86 processors. In 1985, the original 16 bit x86 architecture was extended to 32 bits with the introduction of the i386 processor. It was extended again to 64 bits in 2003 with the introduction of the AMD Opteron processor. 
Intel adopted the 64-bit computing bit architecture in 2004 with the later versions of the Prescott Pentium 4. The different versions are backward-compatible, meaning that a 32-bit x86 CPU can run a 32-bit or 16-bit operating system, and a 64-bit x86 CPU can run a 16, 32, or 64-bit operating system. All x86 CPUs (with the rare exception of some Intel CPUs used in embedded systems) start in 16-bit real mode. A modern operating system (or sometimes the bootloader) switches the CPU into 32-bit protected mode or 64-bit long mode before booting the kernel.
x86 Operating Systems.
Operating systems in magenta run only on x86 processors. Operating systems in blue originated on x86 but have since been made for other processors as well. Operating systems in orange did not originate on x86 and were ported to x86.