# Operating Systems

> Windows, macOS, and Linux - what they're really doing under the hood, from first login to power user.

12 guides.

- [What an Operating System Actually Is](https://themissingmanual.dev/guides/what-an-operating-system-is) _(beginner)_ - The operating system is the manager sitting between your programs and the hardware; understand the kernel, processes, memory, and files and your whole computer stops being a mystery box.
- [The Filesystem, Explained](https://themissingmanual.dev/guides/the-filesystem-explained) _(beginner)_ - A filesystem is the tree of files and folders the OS lays over raw numbered storage; a path is an address into that tree, permissions decide who may touch each file, and a few simple rules explain almost every 'file not found' or 'permission denied' you'll ever hit.
- [The Terminal & Shell, Explained](https://themissingmanual.dev/guides/the-terminal-and-shell) _(beginner)_ - What the black window actually is, the difference between the terminal and the shell, the everyday commands worth knowing, and the real power features - pipes, redirection, wildcards, and PATH - that make typing beat clicking.
- [Processes, Memory & the CPU - Diagnosing a Slow or Stuck Machine](https://themissingmanual.dev/guides/processes-memory-and-cpu) _(intermediate)_ - What '100% CPU' and 'out of memory' actually mean, and how to find the one process that's the culprit - using top and Task Manager you already have.
- [Linux From Zero - For People Who've Never Used It and Are a Little Scared](https://themissingmanual.dev/guides/linux-from-zero) _(beginner)_ - What Linux actually is, how to find your way around its filesystem and install software, how users and permissions work, and how to start and read background services - for someone who's never touched it.
- [Windows for People Who Use It Every Day](https://themissingmanual.dev/guides/windows-for-power-users) _(intermediate)_ - What's actually underneath Windows - the NT kernel, drive letters and the real folder layout, services and the registry, and PowerShell - explained for someone who's used Windows for years but was never shown the manual.
- [macOS Under the Hood](https://themissingmanual.dev/guides/macos-under-the-hood) _(intermediate)_ - macOS is a polished Unix machine - Darwin and the XNU kernel underneath, a real Unix filesystem hiding beneath the Finder, apps that are secretly folders, and a Terminal that feels like Linux because it nearly is.
- [Linux for Servers](https://themissingmanual.dev/guides/linux-for-servers) _(advanced)_ - The leap from desktop Linux to running a real server: a headless box you reach over SSH, services managed by systemd, logs read with journalctl, and a small discipline of users, cron, firewall, and updates that keeps it safe.
- [Editing in the Terminal](https://themissingmanual.dev/guides/editing-in-the-terminal) _(beginner)_ - vim and nano survival: open, edit, save, and (the part everyone fears) quit, without losing your work or your SSH session.
- [How Your Computer Boots](https://themissingmanual.dev/guides/how-your-computer-boots) _(beginner)_ - What actually happens between pressing the power button and reaching a login screen - firmware, bootloader, and kernel handing off control in sequence.
- [Deadlocks Explained](https://themissingmanual.dev/guides/deadlocks-explained) _(intermediate)_ - What a deadlock actually is, the four conditions that must all be true for one to happen, and how to prevent and detect them in real code.
- [System Calls Explained](https://themissingmanual.dev/guides/system-calls-explained) _(intermediate)_ - The controlled doorway between your program and the kernel - why it exists, what happens during one, and why it matters for real performance.