this was an explantion that was given on my cs forums and i think he explains it best these arnt my words but thought you guys would want to see what he had to say.
"In order for Intel to take the crown so they dont look bad to the public eye in the speed wars against AMD, Intel changed the number of bits the CPU processes in a single cycle from 8bits to 6bits. If intel made a p3 2.0GHz and you compared it to the p4 2.0GHz, the p3 would be faster because p3s still process 8bits per cycle.
p3 @ 2,000,000,000 cycles / sec * 8 bits / cycle = 1.6 * 10 ^ 10 bits per second
p4 @ 2,000,000,000 cycles / sec * 6 bits / cycle = 1.2 * 10 ^ 10 bits per second
Then that would utlimately translate down to the number of raw instructions executed per second which we dont need to get into right now.
AMD still processes 8bits per cycle (as the p3s do) and in order not to make themselves look bad in comparison to intels p4 which they "cheated" to appear faster, AMD gives you an equivalent speed rating as if it where a p4. That is the 2000+ number you see packaged on the box. The actual clock cycles, however, is rated lower as you have noticed 1.66 GHz for the 2000+ CPU. If AMD did only process 6bits instead of the 8bits it currently does and just increased the number of cycles as intel did, then the clock cycle speed would in fact be 2.0 GHz or the 2000MHz speed on the package.
p4 2.0GHz = 2,000,000,000 cycles / sec * 6 bits / cycle = 1.2 * 10 ^ 10 bits per second
AMD 1.66 (2000+) = 1,633,000,000 cycles / sec * 8 bits / cycle = 1.3 * 10 ^ 10 bits per second"
from [BC]Twitch.