Ars Technia reports Apple iPad A4 chip is based on ARM Cortex-A8 architecture, though early rumors was Apple adopted the latest Cortex A9 multi-core design. For exact specifications, Apple has not commented. According to multiple sources of Ars Technia Apple uses A4 (besides the PowerVX SGX GPU) back to a single-core Cortex-A8, as currently the case (with a lower clock speed) in the iPhone 3GS, and the third-generation iPod touch is used.
According to Jon Stokes at Ars Technia “ As I watched the videos and read the reports of the iPad in action at the launch event, I was thoroughly convinced that the device was built on the out-of-order Cortex A9, possibly even a dual-core version. But it turns out that the the A4 is a 1GHz custom SoC with a single Cortex A8 core and a PowerVR SGX GPU. The fact that A4 uses a single A8 core hasn’t been made public, but I’ve heard from multiple sources who are certain for different reasons that this is indeed the case. (I wish I could be more specific, but I can’t.)”