A system-on-chip, or SoC, is an integrated circuit that brings most or all of a computer’s major parts onto a single piece of silicon. Where a traditional computer spreads its processor, memory, graphics, and communication functions across several chips on a board, an SoC integrates them into one device. The aim is to shrink size, cut cost and power, and simplify the surrounding electronics, which is exactly what small, battery-powered, mass-produced devices need.
The Espressif ESP32 datasheet is a clear primary example of how much an SoC can integrate. It describes a single chip that combines processor cores with on-chip ROM and SRAM, 2.4 GHz Wi-Fi and Bluetooth radios, and a long list of peripherals including SPI, UART, I2C, I2S, an analog-to-digital converter, and general-purpose I/O pins. It also folds in radio-frequency components such as antenna switches, a power amplifier, and a balun, plus power-management and hardware security blocks, so that a working wireless device can be built around the chip with very few external parts.
A system-on-chip sits on a spectrum with the microcontroller. A microcontroller is itself a kind of small SoC focused on control, while the term system-on-chip usually implies more capability, such as integrated radios, graphics, or higher-performance processors. The boundary is blurry on purpose: the same trend toward integration that produced the modern microcontroller, captured by ever-smaller process technology, kept pulling more functions onto one die.
This is why SoCs are everywhere in modern computing. A smartphone runs on an SoC that combines application processor cores, a graphics processor, memory interfaces, cellular and Wi-Fi radios, and specialized accelerators. A Raspberry Pi is built around an SoC that pairs ARM cores with a graphics and video block. The ESP32 brings the same idea to cheap connected gadgets. In each case the SoC is what makes a small, inexpensive, self-contained device possible, and the design and manufacture of these chips lean heavily on the fabless model, where the company that designs the SoC has it fabricated by a separate foundry.