After they took the iPhone 5s apart, the guys from Chipworks focused their attention on uncovering the mystery of Apple’s A7 chip, which was presented by Phil Schiller, the company’s head of worldwide marketing, as the world’s first 64-bit desktop-class processor.
So what did they find? The transistor-level image of the A7 chip reveals (here: Chipworks’ best guesses) that the CPU is not packed the same way as the A6 chip found in the iPhone 5.
According to Chipworks’ findings, the dual-core CPU and cache make up roughly 17% of the die area, and the quad-core GPU and logic share about 22%.
We know from our analysis of the 32 nm A6 chip that the 6 transistor SRAM cell area was ~0.15µm2, so if we shrink that, we can guesstimate the 28 nm 6T SRAM cell to be ~0.12 µm2. If we further allow a conservative 40%-50% utilization to allow for the row and column circuitry, then we get densities of ~1 MB for the L2 cache, and ~256 KB for the L1 cache.
When we look at the GPU, Anand also makes a convincing argument that the GPU is the four cluster version of Imagination’s PowerVR Series 6, the G6430.
The CPU core is estimated to incorporate 256 KB of L1 cache and 1 MB of L2 cache, but there is no word about how much memory the A7 packs.
One thing that remains a mystery is the fingerprint scanner, but not for long: that specific part of the chip represents high interest for both Chipworks and the rest of the world.