Friday, January 13, 2006

Apple used multiprocessor benchmarks to skew the performance advantage that its Intel-based machines enjoy compared to single-core PowerPC G4 and G5. Apple used the industry-standard SPEC suite components SPECint2000 and SPECfp2000, but here's the catch: Apple used SPECint_rate2000 and SPECfp_rate2000. Both tests spawn multiple parallel benchmark processes and are specifically intended for comparing multiprocessor systems. Single CPU, or single-core machines do positively lousy on SPEC*_rate2000 tests. That's predictable and universally understood. Add a second CPU or a second core and, as you would expect, SPEC*_rate2000 performance on any multiprocessor-optimized test skyrockets compared to a single-processor box.

Apple uses SPEC*_rate2000 tests as a foundation for claims that Intel-based Macs outperform PowerPC G4 and G5 by a factor of 2 to 5. Well, yeah. A dual-core anything outperforms a single-core anything else by a factor of 2 to 5 in benchmark tests that make use of multiple threads or processes, tests crafted specifically for the purpose of stressing SMP-based systems. It's murky marketing, and the sad part is that Apple didn't have to resort to it to make Apple's PowerPC-to-Intel switch look like a smart one. Mac users have no choice, and users also know more or less what to expect performance-wise.