x86 is just the generic term for intel compatible processors. One of the first was the 8086. Then, the 80286, 80386, 80486 (more commonly called 286, 386, etc). Each of these CPU's were advancements in the chip world with new features, instruction sets, etc. If you run a modern Pentium or AMD it would run best if the OS was optimized for i686 architecture, but you can run i486 or whatever. A 486 is the most primitive CPU the newer linux distros will run on. Not bad though considering the 486 came out in the late 80's
