Boot is a chain of trust and control transfers that turns platform reset into a running user-space environment. A common PC path can be summarized as firmware, boot manager or loader, kernel with optional early user space, and the PID 1 init system. Architectures, virtual machines, embedded systems, and containers can use different paths.
Boot the System · Lesson 1
Boot Process Overview
Learn the major handoffs from platform firmware through the kernel to the first user-space process.