The Sony PSP CPU is running on 222Mhz, but the CPU actually can do 333Mhz. Sony capped the clock speed to increase battery life.
There is rumor that for future games a firmware patch of sorts will boost the clock speed to get more performance. The first game to do this should be Gran Turismo 4 Mobile slated for a September release.
More details on GamesRadar.
More Sony PSP Games.
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