What is the difference between RPM - i586, i686, i386 and x86_64

Tell me when downloading Linux are usually invited to choose the i586, i686, i386 and x86_64. The latter probably means that it is a 64 bit processors. And that means the first three?

i386 = 386 e-processors
i486 = 486 e-processors
i586 = Pentium
i686 = Pentium II and older
Of course, the version for i386 processors will be able to work, for example, the Pentium, Pentium because there are all the team's 386 processors, but will not be able to use all its possibilities.

PS "i" in the notation emphasizes that the designation of Intel.

Thanks to an explanation. Why i386 and i486 have found I like or do not see? In fact, 486 will be better!