Every tool you will use as a defender, and every system an attacker targets, runs on an operating system. This module starts with how an operating system works: the kernel, processes, memory and the file system, and why the split between user mode and kernel mode matters for security.
You'll then get practical with Linux: the command line, the permission model (users, groups, chmod and chown) and how services are started and managed with systemd. The module finishes on the Windows side, with the built-in security tools such as updates, Defender, the firewall and BitLocker that make up a baseline for system hardening.
Once you're comfortable on both operating systems, you'll be ready for the next module, Scripting & Automation, where you automate the things you've just learned to do by hand.
The operating system as a resource manager: processes and threads, CPU scheduling, memory management and paging, and how file systems store data.
Reading the read, write and execute bits, changing them with chmod in symbolic and numeric modes, and managing file and group ownership with chown and chgrp.
What systemd is, how it starts and manages services, targets and unit files, and how journald centralises logging, which you'll lean on for investigations later.
Windows Update, Windows Security, virus and threat protection, the firewall, app and browser control, device security, BitLocker and Volume Shadow Copy.