There's a lot of speculation about what's inside the A4, Apple's custom and ultra-power-efficient chip that powers the iPad. Nobody knows for sure because, like all their products, it's a seeeeeecret. Until now.
According to Jon Stokes' well-trusted sources, there is no Cortex A9 dual-core inside Apple's A4, but just a single Cortex A8 and a PowerVR SGX GPU. According to Jon, it's probable that Apple has taken out a lot of the communication, image, and video blocks that the Cortex A8 uses, making it an extremely lean and efficient processor.