In August 2001, AMD declared war on the “megahertz myth” — declaring that for PC users, “the ultimate benefit of processor performance” is not a CPU’s clock speed in megahertz or gigahertz, but “how fast their applications run.” This white paper by Jay Pickett set the foundation (or threw down the gauntlet) for the model numbers identifying current Athlon XP, mobile Athlon XP, and Athlon MP processors.
According to Pickett, AMD and Intel have been following different paths since the days of the K5 and Pentium CPUs, respectively: While the rival processors share the same X86 instruction set and run the same software, their different internal architectures mean that you can’t consider their clock speeds without also considering the work done in each clock cycle (instructions per clock or IPC). In Intel’s case, comparing the Pentium 4 with its Pentium III and earlier predecessors proves the point.
It’s as true for today’s Athlon XP 2600+ (with 2.13GHz clock speed) and 2.53GHz Pentium 4 as it was for the 1.4GHz Athlon and 1.7GHz Pentium 4 put to the test in this article’s benchmarks: Real performance = IPC x frequency, not just frequency. This white paper (in Adobe Acrobat PDF format) makes AMD’s case.