System folders, repair tools and security features of Windows 10 and 11.
What the BitLocker recovery key is, why Windows asks for it, where to find it and how to check protection with manage-bde.
What DISM is, the /CheckHealth, /ScanHealth and /RestoreHealth commands, and how DISM and SFC work together to repair Windows.
What the Windows Driver Store is, why it grows, and how to list and remove old driver packages safely with pnputil.
What SmartScreen is, why it shows 'Windows protected your PC' for new downloads, and how to check a file before running it.
What sfc /scannow does, how to read its results, where the CBS.log is and when to run DISM first.
What Storage Sense does in Windows 10 and 11, which files it removes, and how to configure it safely.
Where Windows keeps temporary files (%TEMP%, C:\Windows\Temp), what is safe to delete and the supported ways to clean them.
What WinRE is, how to open it, what tools it offers, and how to check it with reagentc /info.
What the Windows.old folder is, why it appears after an upgrade, how long Windows keeps it and how to remove it safely.
What C:\Windows\WinSxS is, why Explorer overstates its size, and how to shrink it only with supported DISM commands.