Apple’s path from licensing standard ARM cores to building its own CPU design was well-documented, starting with the company’s decision to purchase PA Semi in April 2008. Its GPU cores, in contrast, have been broadly assumed to be licensed from Imagination Technologies. According to a new report, however, Apple has been building its own GPU cores for years — it’s just that no one noticed.


David Kanter at RealWorldTech spotted the differences by digging into the available architectural manuals for both Apple’s Metal API and Imagination Technologies’ GPU products. There are significant, non-trivial differences between the two. Apple’s hardware is apparently built around 16-bit half-precision registers, while the PowerVR architectures support half-precision, but do not require its use.
 
The advantage of using 16-bit precision in GPUs isn’t really in performance, but in power efficiency. The less data you store in a given register, the less energy it costs to move that data around on-chip. There are also practical advantages in terms of register file size and subsequent power consumption. Overall, the manuals point to fundamentally different architectures — and Apple appears to have gained a tremendous advantage over PowerVR’s baseline technology as a result.