Communications of the ACM
What's Inside the Ipad's Chip?
Apple
Despite widespread speculation, nothing beyond what Steve Jobs announced last week is known about the A4 chip at the heart of the Apple iPad.
Jobs described the chip with typical restraint during the unveiling of the iPad. "It's powered by our own silicon--the one gigahertz Apple A4 chip--it screams," he said, adding that the A4 chip includes an integrated CPU and graphics core on a single system on a chip (SoC).
Soon after the announcement, experts began speculating that the chip was based on the same ARM architecture as the iPhone and iPod touch.
"No official source that I can find has confirmed that the A4 uses ARM," says Tom Halfhill, senior analyst at Microprocessor Report. However, he says, it's logical to assume that the iPad is using a processor based on the ARM architecture. "It makes sense, [because] Apple wouldn't have to port the iPhone OS to a new CPU architecture."
Some have suggested that the chip may be based on the latest and fastest ARM designs, but both the slightly older and slower ARM Cortex 8 and the newer ARM Cortex 9 cores can run at a clock speed of one gigahertz, notes Halfhill. Boosting the speed of an ARM Cortex 8 core--the core thought to run in the Samsung-built chip that powers the iPhone 3GS--to one gigahertz would be possible because the iPad has more room for batteries, allowing engineers to drive the A4 at a higher voltage and therefore clock frequency.
From Technology Review
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