Apple iPad Pro A9X soc has 12-core GPU on board and no L3 cache
Analyzes of the soc used in the Apple iPad Pro have shown that the tablet has a 12-core GPU on board and that the soc is made using TSMC’s 16nm finfet process. It is also striking that this soc, unlike other socs from Apple, does not have an L3 cache.
Apple itself is reluctant to publish too specific technical information about its chips. This information is therefore the result of a die shot made by Chipworks and published by Anandtech. Compared to the A9-soc of the iPhone 6S and 6S Plus, the number of GPU cores has doubled, making it 12. Previous suspicions that the A9X uses the Imagination PowerVR Series7 GPU appear to be correct. The clock speed of the GPU cores is difficult to determine, according to Anandtech, but it is estimated that they are slightly higher than that of the GPU cores in the A9.
Most notably, Anandtech mentions the absence of an L3 cache. The website sees three possible explanations for this. First of all, the memory bandwidth of 51.2GB/s would be so large that there is simply no need for L3 cache to prevent the GPU cores from having to wait for the memory. In addition, the L3 cache on the A9 would be used to save the energy needed for memory operations. However, the iPad Pro has significantly more room for its battery than the iPhone 6S and 6S Plus, so that consideration would count less. Finally, the size of the die might have been a consideration, but since an L3 cache would take up about three percent of the space of the A9X die, that’s unlikely. It is not known what Apple’s actual motivation has been. In any case, the performance of the A9X does not suffer from the absence of the L3 cache.
Some of the specifications of the A9X soc could already be traced through benchmarks. For example, it was already known in advance that the iPad Pro has two Twister CPU cores on board that run at 2.26GHz. In addition, the soc has 4GB lpddr4 memory and the memory bus is 128 bits wide, resulting in the aforementioned memory bandwidth of 51.2GB/s. Given the amount of GPU cores on board, this is not superfluous. The benchmarks showed that the A9X on board the iPad Pro scores significantly better than the A9 that can be found in the latest iPhones. The MacBook from 2015 with Core M-5Y31 CPU also lost out against the A9X of Apple’s latest tablet.