The same full drive looks completely different on Windows and macOS
Both hide space, in different places, with different names. A translation table for anyone who uses both.
Anyone who uses both notices that a full drive is a different experience on each, and that most of the difference is vocabulary rather than substance. This is the translation.
The same thing, different names
| macOS | Windows | What it is |
|---|---|---|
| System Data | System and reserved, plus Other | Everything the storage screen cannot classify |
| Purgeable space | Shadow copy space | Deleted data still referenced by a snapshot |
| Local snapshots | Restore points | Point in time copies for recovery |
~/Library | AppData | Where applications keep everything |
| Sleep image | Hibernation file | Memory written to disk, sized to RAM |
| Swap files | Page file | Virtual memory |
| Trash, per volume | Recycle Bin, per drive | Deleted files still on the drive |
| Spotlight index | Windows Search index | The search database |
| Xcode DerivedData | Visual Studio .vs and obj | Build output and IDE caches |
Where Windows is genuinely worse
- The component store. WinSxS is built from hard links and reports roughly double its real size to any ordinary tool. macOS has no equivalent trap.
- The installer cache. Deleting it breaks uninstalling, which has no macOS parallel.
- Path length. A 260 character limit that breaks tools, which Unix does not have.
- More places. Windows has AppData with three subfolders, ProgramData, and per drive folders, against one Library.
Where macOS is genuinely worse
- Purgeable space. A number that says free and is not, with no interface to inspect it.
- System Data is opaque. Windows at least itemises temporary files by category.
- Full Disk Access. A permission that must be granted before any tool can see everything, which Windows does not require.
- Fewer drives. Most Macs have one volume, so moving things elsewhere is rarely an option.
What is the same
Browsers are the largest application on both. Developer caches dwarf everything else on a working machine on both. Both systems keep deleted files in a per volume bin. And on both, the built in storage screen sorts into categories and refuses to show you a folder tree, which is the actual reason people go looking for a tool.
If you are switching
The habits transfer. Check the hidden application folder, check the snapshots, check the developer caches, check the per drive bins. The names change and the list does not, which is why the Windows order and the Mac one read so similarly.
Common questions
What is the Windows equivalent of System Data?
System and reserved, plus the Other category. Both are what the storage screen cannot classify, and neither can be opened directly.
Does Windows have purgeable space like a Mac?
The nearest equivalent is shadow copy space used by System Restore, where deleted data is still referenced by a snapshot. Windows reports it more honestly, through vssadmin.
Is AppData the same as the Library folder on a Mac?
Broadly yes. Both are where applications keep settings, caches and data, and both are hidden by default. Windows splits it into Roaming, Local and LocalLow.
Which platform hides more storage?
Windows has more places, including the component store and the installer cache, which are both traps. macOS has fewer places but reports purgeable space in a way that is harder to inspect.