Central Processing Unit (CPU)
This is a general-purpose computer. It fetches an instruction, say “add 2”, from memory, applies that instruction to data, say “2”, then commits the result, “4”. Modern phone CPUs overlap these steps, allowing a single core to complete tens of billions of instructions per second.
They contain six to eight cores, some high-performance and other smaller, power-efficient ones; surging when needed and sipping energy the rest of the time.
Graphics processing unit (GPU)
The GPU renders the display you see. The CPU’s step-by-step approach doesn’t work well for controlling millions of pixels, so the GPU is built differently. Thousands of basic processing units work in parallel, each specialised for the repetitive maths that turns code into moving visuals.
The CPU decides what should appear, the GPU calculates how it should look, and passes that to the screen’s TFT layer to illuminate each pixel.
Neural Processing Unit (NPU)
The newest of the trio, appearing in flagship phones around 2017. Binary transistors are very good at maths. Neurones in your brain are better at the fuzzy work of recognising patterns. The NPU is built for the multiply-and-accumulate operations needed for artificial neural networks, using them to recognise the patterns of speech, faces, objects, and somehow power the black magic of generative AI.
Memory
Memory is groups of transistors which can be set as on or off, representing 1 or 0. Billions of these switches work together to store your data.
There are three types. Ultra-fast cache sits inside the CPU. RAM sits just outside, it’s slower but far larger. Both need to be powered to remember. This is working memory, where active software lives.
Flash storage can remember without power. It is slower than RAM, though still dozens of times faster than the spinning hard drives from a decade ago. This is where the software and your files are stored.
Secure Processing Unit
A large city has dark alleyways and crime. Instead of trying to defend every street, your phone has a separate vault processor, holding secrets like your fingerprint and payment authentication data. It keeps them locked up, but gives out single use codes, answering yes or no to questions like ‘is this their fingerprint?’