http://www.appleinsider.com/articles/11/03/13/inside_apples_ipad_2_a5_fast_lpddr2_ram_costs_66_more_than_tegra_2.html

"While the A4 clock speed was steady at 1 GHz," Yogasingam said, "the A5 clock speed varies depending on the application being run. This would indicate an advanced power management circuitry controlling the clock speeds of the cores—something new for the A5 and may explain the use of a different power management IC from Dialog Semiconductor."

这个绝对不只是芯片的feature, 也是系统级别的feature。