# What an Operating System Actually Is

You've used a computer almost every day of your life - opened apps, saved files, complained when it's
slow. But nobody ever sat you down and explained the thing quietly running *underneath* it all - the
operating system. Windows, macOS, Linux: you know their names, but what do they actually *do*?

This guide answers that, from zero. No prior knowledge, no jargon you haven't been handed first. By the
end you'll have a clear mental model of what an OS is and the handful of jobs it does - and your computer
will stop being a mystery box. (This works for non-developers too; it's the broadest on-ramp in the whole
library.)

## How to read this
- **Total beginner?** Read in order - each phase builds on the last.
- **Just want the gist?** Phase 1 alone gives you the core mental model in one sitting.

## The phases
1. **[The Manager in the Middle](01-the-manager-in-the-middle.md)** - what an OS *actually is*: the layer
   between your programs and the hardware, and why it exists.
2. **[The Four Jobs](02-the-four-jobs.md)** - the things every OS does for you: running programs, sharing
   memory, storing files, and talking to devices.
3. **[See It Yourself](03-see-it-yourself.md)** - watch the OS work in Task Manager / Activity Monitor /
   `top`, follow what happens when you press the power button, and see how Windows, macOS, and Linux are
   the same idea in different clothes.

> This is the foundation for the rest of the Operating Systems track - the filesystem, the terminal,
> processes and memory in depth, and guides for Linux, Windows, and macOS each build on the model you
> install here.