The iPad 4 houses a 30% larger silicon die than its predecessor
The A6X SoC (system-on-a-chip) used in the iPad 4 has been dissected by Chipworks. The silicon experts used electron microscopes to determine how the A6X was manufactured, calling it "a very new beast."In their teardown of the new Apple chip, the company found that “this is not just an A6 with a couple minor tweaks. Being a full 30% larger than its predecessor, the A6X is considerably bigger on the GPU side. On the CPU front, the A6X is identical to the A6, Chipworks reports.
“This is not surprising given that the prior CPU used custom layout techniques, and therefore it would be a huge amount of work to redesign so soon. Much of the extra area has gone to the GPU cores which are up from 3 to 4,” says the company.
In fact, each GPU core is much larger, doubling the overall occupied area.
“So we see that of the 29 mm2 of new area on the A6X, a full 18.6 mm2 is the result of the increased quantity of graphics processing. Impressive!” the savvy geek squad notes.
The GPU cores are actually split into sub-cores themselves. Each one is sub-divided into 9 sub-cores - “2 sets of 4 identical sub-cores plus a central core,” according to the teardown analysis.
Chipworks theorizes that, “This could be done to allow for more efficient parallel processing, or to allow for a higher maximum clock rate. In either case, these GPUs should result in some blazing graphics on your iPad,” the company reports.
Another cool finding noted in the teardown report is that the A6X has double the SDRAM interface width of the A6.
Additionally, “Apple has reduced the number of core PLLs needed from 9 on the A6 to 8 on the A6X,” says Chipworks, pointing out that these have been moved close to the middle.
The consensus at Chipworks (regarding this change) is that Apple was attempting to “gain better control over clock skew across the chip.”
Lastly, although there are also some new interface blocks present in the A6X, “many of the analog and interface cores have been reused from the A6,” Chipworks confirms.
For their full analysis, complete with photos, visit Chipworks here.