A dissection of the A4 chip
Apple designed for the iPad reveals that it's fairly conventional, incorporating a single core CPU - possibly the same one used in the iPhone 3GS - and some DRAM in a triple-layer "package-on-package" (PoP) design. Because the system-on-a-chip included the core and memory on a single piece of silicon, though, heroic measures were needed to look inside, including X-raying, soaking it in an acid bath and using a grinder to cut into the A4.
The guys at iFixit
have done methodical teardowns of everything from cameras to guitars to mopeds
. They did one on Apple's newest device on Saturday
, revealing elegant engineering and a fancy case design, but nothing extraordinary. One black box remained, though: Apple's homegrown A4 system-on-a-chip. The iFixit guys had done a crude dissection of the iPhone's CPU with a band-saw back in 2007, but for this job they needed more advanced techniques, so they went to Chipworks, which does reverse engineering and patent protection work for major Silicon Valley manufacturers.
First, the A4 was X-rayed from the bottom and sides, showing the fine wirebond interconnects between the three layers. Then, the chip was dipped in acid to remove the ceramic outer layer, and was slowly ground down to reveal each individual die. The two DRAM modules had Samsung markings on them, as expected, but the CPU itself was unmarked. This indicated to iFixit's Kyle Wiens that "Apple is in firm control of the semiconductor design," rather than it being a result of Samsung engineering as is the iPhone 3GS CPU.
The analysis supported clues that ZodTTD
already identified from his dump of the iPad's I/O registry tree
, indicating that the A4 is indeed a single-core processor. This strengthens the case that the CPU is a Cortex-A8, rather than a Cortex-A9 as had been theorized. The GPU can't be conclusively identified from looking at the logic, but based on benchmarks it's believed to be a PowerVR SGX 535.
The conclusion? "There's not much revolutionary here," Kyle Wiens wrote, noting the A4 isn't all that different from the Samsung processor Apple uses in the iPhone. Only the power characteristics seem to have changed significantly, with the SoC drawing about 2.5 watts on average to give the iPad its 10 hour battery life.
image via iFixit