Why buy an AMD processor when and Intel one has a higher clock speed?
It is true that AMD's processors run at slower clock speeds (i.e., AMD Athlon64 3500+ runs at 2.2GHz, and a comparitive, the Intel Pentium4 550 runs at 3.4GHz). It is also true, as noted above, this does not matter. The point is that Clock speeds are not the be all and end all factor to determine performance
The architecture of the 2 manufacturers products are totally different. AMD's chips are designed such that they have a shorter pipeline, this being a sort of conveyor belt of instructions, than Intel's chips. This means, again in lay terms, that AMD's processors can perform more work per cycle which is why they get away with slower clock speeds and still offer comparable (and sometimes superior). So you see that clock speeds are not to be used to compare between the two chiptypes.
Back in the days of the AthlonXP, AMD took to naming their chips using something called a performance rating. Officially this was meant as a meant of measuring the performance of the chips, however consumers began using the numbers to compare the XPs against the Intel's Pentium4 processors(which was AMDs real intent for the naming system). Thus, people often drew a comparison between, say an AthlonXP 3000+ and a Pentium4 3.0GHz, likewise the AthlonXP 2800+ was to be compared to the Pentium4 2.8GHz. To a degree, these comparisons were valid and held however there are many exceptions (i.e., the ratings do not compare as evenly as the clock speeds begin to get higher)
Interestingly Intel who long named there chips after clock speed, also use an indexed scale for processor designation. See
Intel's website for more details. If it's not obvious, this should be an indication that clock speed alone is having a less and less role in overall chip performance.
Recap
* Clock speed don't solely determine performance
* AMD operate at lower clock speeds
* AMD and Intel use a performance rating naming system.
