Ubuntu APT Package Cache (/var/cache/apt/archives)
/var/cache/apt/archives stores downloaded .deb package installer files. Running sudo apt clean is safe and reclaims gigabytes of disk space.
Installers & Updates Files
Windows Update cache, leftover MSI files
Flatpak Package Cache & Unused Runtimes (/var/lib/flatpak)
/var/lib/flatpak stores Flatpak desktop apps and runtimes. Pruning unused runtimes with flatpak uninstall --unused is safe and frees space.
Panther Folder (C:\$WINDOWS.~BT\Sources\Panther)
The Panther folder stores setup and upgrade log files for Windows installation. Deleting Panther is safe and frees up hidden upgrade logs.
Ubuntu Snap Package Cache (/var/lib/snapd/snaps)
/var/lib/snapd/snaps stores old disabled versions of Snap packages. Removing old revisions is safe and frees up gigabytes on Ubuntu.
Windows Installer Folder (C:\Windows\Installer)
C:\Windows\Installer contains essential MSI application patch files. Never manually delete it, but orphaned installers can be safely cleaned with official tools.
DeliveryOptimization
A folder Windows uses to share Windows Updates with other PCs on your network or the internet. Safe to clean via Disk Cleanup.
SoftwareDistribution
The folder where Windows Update downloads new updates. Safe to clean if updates are failing, but should not be deleted randomly.
$Windows.~BT
Leftover installation files from a previous Windows upgrade. Safe to delete using the Disk Cleanup tool.