Initially, AMD's PR nomenclature of the Athlon XP models was based on the chips performance compared to that of the Athlon 1000 (1000MHz Thunderbird), and not to any Intel chips, as often rumored. So, an Athlon XP 1700 had 1.7x the "performance" of an Athlon 1000. However, the Athlon PR-rating system was later changed, with the introduction of the 2400+ and 2600+ models.

However, this often held relatively true comparing the PR model number to MHz of an Intel P4 core; as the PIII 1000MHz was almost neck-n-neck with the Athlon 1000, and for the most part the pentium chip's performance maintained a correlation to its raw clock speed.

From Wikipedia:
Quote:
Unable to compete with the raw clock speeds offered by the P4, from the start of the Athlon XP era, AMD began using a nomenclature that compares performance of the Athlon XP, with that of an earlier Thunderbird core revision. In reality most people saw the model numbering scheme for what it was - an attempt to disguise AMD's clock speed difference compared to the P4, and accentuate on the pure performance of chip, which was equal to P4. It did, however, make some consumers think that Intel's high clockspeeds did yield superior performance over the Athlon XP. This definition began to be applied more loosely over time as AMD struggled to compete with the ramping clock speeds of the Northwood core (>3.0 GHz). The credibility of the scheme was only saved by the arrival of the K8, where model numbers once again correlated more reasonably to actual performance.
With that all said, the numbers really dont mean anything anymore. An x2 3800 does not equal an Athlon 64 3800, which does not equal a P4 3.8GHz. All in all, it's just marketing.