A system on chip integrates most of what a device needs on a single piece of silicon. For IoT the defining addition is the radio: a wireless SoC bundles a microcontroller or application processor with a Wi-Fi, Bluetooth, Thread or cellular modem, plus security blocks and sometimes a small NPU for on-device inference. The ESP32 is a well-known example at the low end; smartphone chips sit at the high end of the same idea.
Integration lowers bill-of-materials cost and board area and simplifies certification, since the radio design is largely done by the chip vendor. The price is flexibility: you cannot swap the radio without changing the chip, and a SoC’s lifecycle is set by its maker. Designers who want a tested module rather than a bare chip step up to a system on module or an IoT module.
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