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A4 is a System-on-a-Chip, or SOC, that integrates the main processor [ARM Cortex-A9, identical to ones used in nVidia Tegra and Qualcomm Snapdragon] with graphics silicon [ARM Mali GPU], and other functions like the memory controller on one piece of silicon - not unlike what Intel is trying to achieve with its future "Moorestown" Atom processor that debuted inside LG's Smartphone.
According to reports, neither the Cupertino company nor PA Semi (which was purchased by the former) had anything to do with the A4 processor. Turns out that Apple's newest baby is an ARM Cortex-A9 processor with an ARM Mali GPU, which is similar to the ones used by the Nvidia Tegra and Qualcomm Snapdragon platforms.