It stems from the Intel 8086 (x86) architecture in the IBM PC in 1981. Following is a brief history of PC CPUs, starting with the most current. Starting in 1994, AMD introduced its first Pentium ...

The successor to the Pentium Pro from Intel. Pentium II refers to the CPU chip or the PC that uses it. Code-named Klamath, the Pentium II was a Pentium Pro with MMX multimedia instructions.

Although chips including Intel's Pentium 4 series could be overclocked ... The AMD FX-4170 was the first consumer desktop CPU to reach 4 GHz out of the box without any need for overclocking.