The iPad mini with Retina Display rounds out the three platforms that use Apples A7 SoC. Although both the iPad Air and iPhone 5S use the A7, the minis implementation is closer in nature to the iPhone. The iPad minis SoC has always used the same package-on-package (PoP) assembly as the iPhone, with DRAM stacked on top of the SoC itself (1GB in this case). The benefit is obviously a reduction in board area, the downsides have to do with cost and thermals. Thats the first similarity between the minis A7 and the iPhones A7.
The second is one of frequencies. While the iPad Airs A7 runs its two Cyclone CPU cores at up to 1.4GHz, the SoC in the iPad mini and the iPhone 5S runs at up to 1.3GHz. That might sound like a minor difference, but its far more pronounced when you look at what happens to frequency when youre running heavy workloads.
Once again I turn to a fairly heavy CPU workload to plot performance over time. This is a multithreaded workload, slightly modified from what we used in the iPad Air review, designed to make the CPU cores consume max power. The scale is linear and the workload is the same across all devices, so what youre effectively looking at is a graph of thermally bound CPU performance over time across all three A7 implementations.
Being the largest device (and the only device with a metal heat spreader and no DRAM stacked on top), the iPad Air obviously maintains the highest frequencies for the duration of the test. The iPhone 5S, with a significant reduction in internal volume (and a PoP SoC) reduces its CPU frequencies early on in order to keep skin temperature down and properly manage thermals. The iPad mini with Retina Display falls between the two, with its performance curve more closely following that of the iPhone 5S.
Although the mini has a similar max operating frequency to the iPhone 5S, it is a faster device thanks to it being less thermally constrained. Similarly, the iPad Air can be much faster than its clock speed would otherwise imply. If youre wondering why Apple has been so focused on building its own SoCs and CPU architectures, this is the reason why. Theres a fixed amount of power you can dissipate in the form of heat in these mobile devices while still maintaining a good user experience. Performance per watt is the gating metric for success in mobile, and shipping high IPC/low frequency dual-core SoCs at 32/28nm is the best optimization available to a company like Apple today.
As youd expect, our browser based CPU tests show the minis A7 performing in between the iPhone 5S and iPad Air. None of these tests are anywhere near as stressful as our thermal test from above, so we dont see exaggerated differences in performance between the platforms. For most, I suspect you wont notice a huge performance difference between the mini and Air. Those who are heavier users (e.g. audio mixing, 3D gaming, etc
), there will be a performance difference between the two iPads.
//mommy dearest
