5 lessons
You press the power button. Here's the very first thing that happens.
Before any operating system, before any program, before even the first instruction - there's a reset signal, a fixed address, and a tiny piece of permanent firmware. This is where every single boot begins.
How does a tiny piece of firmware find and load an entire operating system?
Firmware doesn't know anything about Windows or Linux. Here's the small, deliberate handoff chain - firmware to bootloader to kernel - that gets a full OS from a cold disk into running RAM.
The kernel wakes up - taking over the hardware you spent five modules learning
The instant the kernel's first instruction runs, it inherits raw, unmanaged hardware and has to organize all of it from scratch - memory, interrupts, devices, and the very first process - before anything you'd recognize as an "operating system" exists.
You double-click an app. Now trace every single thing that happens.
From a click, to a process being born, to the very first instruction fetched, to your first keystroke reaching the screen - every mechanism from every earlier module, chained together in the exact order they fire.
While your program runs, dozens of other things are happening that you never asked for
A running computer is never doing just one thing. Timer interrupts, context switches, DMA transfers, cache refills, DRAM refresh - here's the constant, invisible background activity happening underneath the program you think has your CPU's full attention.