Megahertz will take you only so far. Desktop processors topped the 1GHz mark in 2000, 2GHz in 2001, and 3GHz in 2002. Nearly five years later, we've yet to see a chip leave the factory clocked at 4GHz. Power demands and heat concerns meant that AMD and Intel couldn't simply keep ramping up clock speeds with each new CPU generation without running into design obstacles with desktops and, especially, with notebooks.
Having come to the end of the megahertz rope, Intel and AMD looked to other methods for increasing processing power while maintaining or improving efficiency, the most significant of which was increasing the number of processing cores on a CPU. The multicore era began in spring 2005 with Intel's Pentium D 800 dual-core chips, and AMD soon followed with the Athlon 64 X2 chips. AMD dominated the initial round of head-to-head benchmarks, and Intel's subsequent Pentium D 900 series, released in the autumn of 2005, did little to dampen the enthusiasm for AMD's X2 line.
