Can you elaborate? I do remember clockspeed being the main thing you looked at and then being surprised that changed, but didn't really have any insight.

Parent is probably referring to ~2000 to ~2010.

Generally speaking, AMD had some more advanced microarchitecture features than Intel, leading to better per-clock performance.

Intel marketing struck back by emphasizing GHz, GHz, GHz. At least until Pentium 4 scaling hit a brick wall.

Then, a chip was sold as a "Pentium 4" "2.8 GHz" (or a "Pentium II" "300 MHz"). No other codes.

By the end of that range, the multicore era had started, and both Intel and AMD had moved to new systems of processor labelling.

Pipelining was really kicking off in a big way and suddenly IPC made as big a difference at a time amd led in that regard as clock speed so amd started numbering their cpu models with a number that was based on the MHz they'd expect an Intel CPU to need to reach to match it.

Of course intel also released new CPUs and AMD didn't want their newer CPUs to have lower numbers than their old one, so that number eventually got inflated.

As others mentioned, Pipelining resulted in scenarios where Other manufacturer's CPUs had a lower clock rate but 'comparable' performance.

There's two main Eras of this;

During the P5/P6 Days, AMD, Cyrix, and NexGen made CPUs with 'PR' ratings, based on what they felt their CPU's compared to.

Ironically, this first era is probably why folks got so soured on 'PR ratings'; As far as the AMD K5 and Cyrix 6x86 went, These numbers were based more on integer performance, additionally Intel's P5 had a very novel (at the time) pipeline that some Game developers were optimizing for (Quake comes to mind here.) For NexGen the situation was even worse, in that some of their models completely lacked an FPU.

All those factors together made consumers a bit more wary of PR ratings for quite a long time.

Thankfully, AMD Bought out NexGen, took their arch and made it into the K6, which was very competitive with the P5 Clock for clock, and PR ratings went away.

They came back in the days of the Palomino K7s, but what a lot of people might not remember is that the Athlon XP's PR ratings were technically supposed to relate to a Thunderbird core. IOW, an Athlon XP 1800 was supposed to be 'equivalent' to an TBird Athlon running at 1800Mhz.

But, of course, PR ratings drifted again, as they tended to... and now we are in model number hell.