A fast chip in a phone only helps if the phone can keep it running fast. The iPhone 18 Pro and iPhone 18 Pro Max are turning out to be among the most consequential upgrades among smartphones: the first variable-aperture camera on an iPhone and the highest sustained performance in iPhone history. Smartphone chips are designed to sprint, but a slim glass-and-metal slab has limited room to get rid of heat, and performance drops once the silicon gets too hot. With the A20 Pro, Apple has tackled both problems. It has built a more powerful chip and also changed the way the chip sits inside the phone so that it can hold its peak speeds for longer.
“With A20 Pro, we’ve taken huge steps with a brand new architecture, and paired with incredible efficiency across the system,” Anush Venkatesan, senior director, iPhone product marketing at Apple, told us over a video call. “We feel like we’re delivering a new standard for computing on a smartphone.”
The chip powers the iPhone 18 Pro, the iPhone 18 Pro Max and the iPhone Duo, Apple’s first foldable iPhone. Most of the talk around the A20 Pro has been about benchmarks. But there’s much more to the story, like how Apple ended up changing the phone’s packaging and internal structure.
What the A20 Pro brings
The A20 Pro is Apple’s first system-on-chip (SoC) made on a 2-nanometre process. Dan Murray, VP Silicon Engineering, Apple, said the move to 2nm brought “greater transistor density, improved power efficiency, and higher performance”. Apple used those gains across the whole chip.
One of the biggest changes is in the six-core CPU. For the first time, Apple has brought the “super cores” from its M-series Mac chips to the iPhone. According to Murray, they deliver performance “rivaling desktop performance for short bursty workloads, like launching an app or loading a webpage”. Alongside the two super cores are four efficiency cores that handle sustained work and background tasks while using less power. It also includes integrated neural accelerators tuned for low-latency AI tasks.
The GPU now has seven cores, one more than before, and Apple says it is up to 40 per cent higher graphics performance than the A19 Pro’s and more power efficient. Murray said the micro-architectural improvements were aimed at high-end games. The GPU also carries Apple’s second-generation neural accelerators, which have higher throughput and handle much of the on-device AI work, including advanced image generation.
Apple has made a bigger change to the Apple Neural Engine. The A20 Pro has a new Dual 16-core Neural Engine, with 32 cores in total, which doubles the AI processing power of the A19 Pro. The two engines can work independently or together in what Apple calls “bonded mode”. Murray explained that having two engines lets Apple “offer significantly higher performance in the same power envelope by running it [at] lower voltage”. He said this matters for on-device AI tasks such as Siri and for the camera’s new computational imaging pipeline.
Memory bandwidth is up 50 per cent, because the memory interface has been widened from 64-bit to 96-bit LPDDR5X. Murray said this “gives huge benefits for memory intensive workloads”, including on-device AI and high-end gaming.
AI comes up repeatedly because Apple sees it as a task for the whole chip. “We’ve recognised that not all AI workloads have the same compute needs,” he said. The Neural Engine, GPU and CPU all have a part to play, and Apple’s AI frameworks let developers send each task to the most suitable engine.
(Left to right) Internal view of the front of iPhone 18 Pro, internal view of the front of iPhone 18 Pro Vapour Chamber, internal view of the back of iPhone 18 Pro Vapour Chamber with battery, and internal view of the back of iPhone 18 Pro display. Picture: Apple
The iPhone Duo version of the chip has some changes for the foldable. A second display engine runs the 7.6-inch inner display and the 5.4-inch outer display at the same time, so moving between them feels seamless. The chip also supports placing the FaceTime camera beneath the inner display, so that screen has no cut-out.
The gains also show up in battery life. Apple says the iPhone 18 Pro Max has the largest increase in battery life ever on an iPhone, thanks to more efficient silicon and a larger battery.
That extra power comes at a cost. “We can’t avoid the fact that all this compute capability does consume power, and that power, in turn, generates heat, and we need to extract that heat from the silicon,” Murray said.
Until the A20 Pro, every iPhone chip used package-on-package (PoP) construction. In this design the DRAM sits directly on top of the SoC. Stacking saves board space, but the memory acts like a lid that traps heat in the processor underneath.
For the A20 Pro, Apple has brought over a packaging technique inspired by the M-series Mac chips called wafer-level multi-chip module (WMCM). The SoC and the DRAM now sit side by side rather than one on top of the other. This takes up more board space, and Murray said the silicon team worked closely with the system team to make room for it. The benefit is that the memory is no longer in the chip’s thermal path, and the SoC connects directly to the phone’s vapour chamber. “This means we can run longer in higher performance states, which provides a meaningful benefit to users,” he said.
Four pillars of cooling
Banafsheh Barabadi, senior manager, Thermal Product Design at Apple, said the new packaging changed what her team could do. “For the first time, we could actually couple directly to our thermal solution from the silicon, and we designed the entire system around it,” she said.
Barabadi described the thermal system as resting on four pillars. The first is the silicon itself. With WMCM, the chip now sits on top of the logic board, which gives it a direct thermal path to the vapour chamber and removes the bottleneck created by the old stacked design.
The second is a new thermal interface material that Apple calls “metal over foam”. It links the SoC directly to the vapour chamber and is flexible enough to meet the phone’s strict mechanical requirements while still removing heat efficiently. Barabadi said it took “months of development to get this material property exactly right”.
The third is the vapour chamber, now in its second generation. It has three times the surface area of the one in the iPhone 17 Pro and a new internal wicking structure that circulates more deionised water. Because the silicon now touches it directly, Apple can make use of the whole surface. The vapour chamber also now forms the phone’s central structure. “It is simultaneously our primary thermal solution and the back part of the mechanical system,” she said. It is made from 80 per cent recycled stainless steel.
The fourth pillar is an industry first: nano-twin copper used as the display plate. The material offers “a unique combination of mechanical strength and thermal conductivity that hasn’t been previously available in a smartphone”. Together with a highly conductive graphite sheet, it spreads heat across the display area and reduces hot spots.
The iPhone 18 Pro models deliver up to 40 per cent higher sustained performance than the previous generation, the highest sustained performance yet on an iPhone. Compared with the iPhone 16 Pro, the gain is nearly double. The improvements show up in long-running tasks such as gaming and video recording, in short bursts such as on-device AI inference, and in charging.
Barabadi said the iPhone Duo “presented an entirely different set of challenges”. Opened, it is the thinnest iPhone ever, in a foldable form factor that was, at one point, widely considered thermally impossible. Its vapour chamber is custom-designed and integrated into the phone’s chassis.
The hardest problem was getting heat from one half of the phone to the other. Apple’s answer is a flexible graphite sheet that runs through the hinge and links both sides. She said the material had to survive repeated folding while keeping its thermal conductivity and structural integrity for the life of the product, which took “significant co-engineering between our thermal and mechanical teams”.
“What I find most compelling about the work is none of that is visible to the user, and that is exactly the point,” she said.
Now it’s time for you to go and pick up the iPhone 18 Pro (or Pro Max). And if iPhone Duo is on your mind, pre-order begins on October 16 and the phone will be available from October 23, which puts it in Indian stores for the festive season. In other words, you can take some incredible photos during Diwali.