• Nitesh

The Retina Macbook Air and 2018 iPad Pro - Awkward Silicon Juxtaposition

Updated: Jan 10, 2019

On October 30th, Apple unveiled three new devices - a long awaited Retina refresh for the Macbook Air, third generation iPad Pros, and a new Mac Mini. The Mini is an interesting desktop, now with 'Full Fat' 65 watt desktop Coffee Lake processors, but it was the awkwardness of the silicon of the Air and the iPad Pro that interested me.

First, the Macbook Air. What's notable about the Air is that it moved down a wattage class, from the previous 15 watt chips down to the Y series and appearing to run at 7 watts, albeit with a fan which should forstall dropping turbo clocks longer than the fanless systems these Y series parts usually find themselves in. That's not to say it'll end up slower than the old Air, for the multi-generational jump in architectures since.

The new Macbook Air was incorrectly reported by some to be fanless - a fan was shown clearly in the keynote

What this fanless tier CPU with a fan also means is that it misses out on the largest gain in the U series chips, the move from two cores to four, which was the most substantive change in this class for the 8th generation processors. Matching up the core count, base, and boost clocks with Intels Ark database, the processor in question appears to be the Core i5-8210Y. Geekbench results have also trickled out since the initial showing.

Not a regression from, though not massively faster than, an Core i7-5650U Macbook Air from years prior (3592 Single-Core, 6883 Multi-Core). Again, the three generation gap in processors more than equalling the step down in rated TDP. Here's where it gets a little funny - the A12X, older brother to the A12 in the iPhone XS and XR, was also introduced on the same day, with twice the large cores as the A12, and twice the memory bandwidth bit width. Here's what Anandtech had to say about the A12 found in phones with less power budget -

Monsoon (A11) was a major microarchitectural update in terms of the mid-core and backend. It’s there that Apple had shifted the microarchitecture in Hurricane (A10) from a 6-wide decode from  to a 7-wide decode. The most significant change in the backend here was the addition of two integer ALU units, upping them from 4 to 6 units.
Monsoon (A11) and Vortex (A12) are extremely wide machines – with 6 integer execution pipelines among which two are complex units, two load/store units, two branch ports, and three FP/vector pipelines this gives an estimated 13 execution ports, far wider than Arm’s upcoming Cortex A76 and also wider than Samsung’s M3. In fact, assuming we're not looking at an atypical shared port situation, Apple’s microarchitecture seems to far surpass anything else in terms of width, including desktop CPUs.

A 7-wide decode engine and 13 execution ports, making the A12's big Vortex cores wider than even desktop CPUs - all in your pants. Perhaps you see where this is going.

Friendly enough looking

Now for the iPad. The X series of Apple silicon has long been where they added GPU execution resources and doubled the main memory bandwidth to feed more screen pixels, as well as increased core counts over iPhone processors in some cases (A8X, A10X, and now A12X). The processors even when not bumped in core counts have also enjoyed more thermal headroom over their phone brethren, allowing higher clock speeds. The A12X sits at a 4+4 configuration with full Heterogeneous Multi-Processing in tow, meaning all 8 cores can run on a task at once if the scheduler sees fit. The results? Impressive is an understatement.

Intel orders another drink

Here we have a fanless 11 inch tablet not just casually embarrassing the Intel Y series, but also strolling past much of the U series and even getting within shadow distance of the 45 watt processors in the 15 inch Macbook Pro.

So how the Air, introduced on the same day and at a higher entry point than the iPad Pro compares? Not so pretty.

Not a single subtest is won by the Intel part

Woof. Now, these systems aren't entirely comparable, and once you add in the smart keyboard and Apple Pencil 2 as well as match the storage tiers, the price gap largely evaporates. iOS still has some severe limits on being a primary productivity machine - it got external display support, great, but you still can't use an external hard drive directly with the USB C port, and if you could you could still not work directly off the files on it. There's also no cursor support, no Xcode, and so on. But in terms of raw compute performance per dollar, the iPad is far and away the best bang for your Apple dollar, and if iOS13 addresses the above shortcomings, could more seriously threaten the Macbook and Macbook Air.

Unless Intel pulls some serious coups in low wattage system performance in the next few years, there's really only one reversal to this I see, and that is an ARM Macbook switch, already to much industry speculation. Apple silicon, but unbound from the limits of iOS, with active cooling, and more wattage to work with - now that's something I cannot wait to see.

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