Check out the Intel Quark, it was a <50mhz x86 that was resized and re-done on a smaller feature fab and runs on a watch battery (its a bios battery), a full x86 SOC!
I dont know what feats of engineering went into it, it is discontinued, but it is a very tiny x86
I dont know what feats of engineering went into it, it is discontinued, but it is a very tiny x86