This chip runs at 1.6GHz by default but can turbo up to 2GHz with two cores active and 2.3GHz with one core active. The screenshot above is from a 1.6GHz Core i5 on an 11-inch MacBook Air. The first is output from Lion's boot process, note the line that begins with AppleIntelCPUPowerManagement: I offer you three pieces of evidence that support the theory that Apple is not artificially limiting clock speed on any of the MacBook Air systems I've tested. Lion got rid of the 32-bit kernel so my previous trick to run MSR Tools to measure clock speed stopped working. All subsequent Intel architectures have supported Intel Turbo Boost, a feature we investigated extensively in our 2011 MacBook Pro review earlier this year. Unused cores could be power gated, effectively shutting them off, and the resultant available TDP could be used by turbo boosting active cores. Nehalem came along and introduced power gating to x86 CPUs.
We needed a way of shutting down cores to free up TDP and dynamically adjusting clock speed. When using all of your cores the tradeoff was worth it, but when only one or two were in use, it wasn't. This meant that your dual-core CPU would run each core at a lower frequency than your single-core CPU, and your quad-core CPU would run at an even lower speed. TDPs couldn't go up (laptops weren't going to double in size) but you now had multiple cores sharing the same TDP, so each core had to dissipate less heat. Then multicore CPUs came around and made things more complicated. In the old days this was pretty simple, you had a single core and a single thermal design point (TDP) that you had to hit. Those limits are shared with manufacturers who then spec power supplies, cooling systems and cases that can handle those CPUs. All CPUs are designed to certain power and thermal limits. First a quick refresher about what Turbo Boost does on Intel CPUs. Letting my guard down wasn't something I was interested in doing so I went about verifying Turbo on the new Air. Since then I've been quite concerned about Apple playing clock speed games with its systems, but thankfully since then we haven't seen any similar issues.
Instead the chip typically ran at or below 1.4GHz, allowing the second generation 11-inch MacBook Air to outperform it. The original MacBook Air had a 1.86GHz Core 2 Duo that pretty much never ran at 1.86GHz.
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