Help, there’s a Mac on my network (2): where’s the C drive?

Episode 2 of the series Help, there’s a Mac on my network.

What happened

Tuesday morning, quarter past nine. Marieke was standing at Ruud’s desk with her MacBook Air under her arm. “It says my storage is almost full. Could you take a look? And where are my files, actually? I saved a quote yesterday and now I can’t find it.”

Ruud put down his mug (“Have you tried turning it off and on again?”) and opened the Mac. Twenty years of experience told him exactly what to do: open File Explorer, This PC, check the free space on C:, then head to C:\Users\marieke\Documents.

There was no File Explorer. There was a cheerful little face in the Dock. Ruud clicked it and got a window with “Recents”, “Applications”, “Desktop” and “Downloads” down the side. No C:. No D:. Not a single letter.

“Where’s the C drive?” he asked nobody in particular.

“There isn’t one,” Marieke said brightly. “I found that very calming.”

Ruud clicked around some more. He found something called “Macintosh HD” with “Applications”, “System”, “Users” and “Library” inside. But when he tried to poke around in “System” it felt like visiting a museum: look all you like, don’t touch. “In Windows that was just under C:\Windows,” he muttered.

Sam walked past with a roll of tape for Karin and stopped. “Mind if I…?” He pressed Shift, Command and G, typed ~/Documents, and there was the quote. Then Command and space, “Storage”, Enter. A coloured bar showed 120 GB going to something called “System Data” and most of the rest to a OneDrive folder.

“How do you know all this?” Ruud asked.

“I wrote my thesis on a Mac. It was always full too.”

What’s really going on

Windows thinks in drive letters. Every disk, partition or network share gets a letter, and C: rules them all. macOS thinks like Unix: there’s one tree that starts at / (the root), and everything hangs off it. A USB stick, a network share or a second disk doesn’t get a new letter. It becomes a folder in that tree.

The internal disk in a modern Mac is formatted with APFS. It holds a container, and that container holds several volumes that share the free space between them. The two you need to know:

• The system volume (usually “Macintosh HD”). This is macOS itself. It’s read-only and cryptographically sealed, so there’s nothing to “clean up” there, and that’s the point. Think C:\Windows with a lock on it that even the admin can’t casually open.
• The Data volume (Macintosh HD - Data). This is where users, the apps you install and all the settings live. Finder shows the two together as one disk, so in day to day use you barely notice.

Marieke’s stuff lives in her home folder: /Users/marieke, or ~ for short. Inside are Desktop, Documents, Downloads, Pictures and a hidden Library folder (~/Library). That last one is the AppData equivalent: settings, caches and app data. Apple hides it because users have no business in there. Admins do.

Then OneDrive. The OneDrive app uses the macOS File Provider, which means the files live in ~/Library/CloudStorage/, in a folder named something like OneDrive-BoldermanInstallatietechniek. Google Drive and Dropbox end up in the same place. iCloud Drive is the exception: it lives in ~/Library/Mobile Documents. You don’t need to memorise these paths, because Finder lists them in the sidebar under Locations.

You don’t check storage through the properties of C:, but in System Settings. “System Data” there is a catch-all for anything that doesn’t fit another category: caches, logs, local Time Machine snapshots and more. Don’t panic when that number moves around. Part of it is “purgeable” and macOS frees it up by itself when space is needed.

How to fix it

Checking storage

1. Choose Apple menu > System Settings > General > Storage. You get a bar per category plus recommendations for freeing up space.
2. Click the info button next to a category to see what’s in it, for example large files in Documents.
3. To see the container and volumes, open Disk Utility and choose View > Show All Devices.
4. Prefer Terminal? df -h shows free space, diskutil apfs list shows the container and its volumes.

Finding files like an admin

• Go to Folder: Shift+Command+G. Type a path like ~/Library/Application Support or /Volumes. Tab completes, just like in a shell.
• Show hidden files: Shift+Command+period in a Finder window. Press it again to hide them.
• Open Library: hold Option while the Go menu is open and Library appears in the list.
• Path bar: View > Show Path Bar (Option+Command+P). The bottom of the window shows where you are, and every part is clickable.
• Get Info: select a file and press Command+I. It’s the Mac version of Properties: size, location, permissions and which app opens it.
• Computer: Shift+Command+C opens the view closest to This PC. You can also add the home folder and internal disk to the sidebar in Finder > Settings > Sidebar.
• Spotlight: Command+space and part of the file name. Often quicker than browsing folders.

External drives and network shares

A USB drive shows up in the sidebar and, if that’s switched on in Finder > Settings > General, on the desktop. In the tree it lives at /Volumes/name. Eject it with the little button next to its name, not by yanking the cable.

You don’t map the department share on the file server as S:. Instead go to Finder > Go > Connect to Server (Command+K), type smb://FS01/afdeling, click Connect and sign in with the Entra or domain account. The share appears under Locations and at /Volumes/afdeling. To have it come back after a restart, drag it into System Settings > General > Login Items & Extensions, under Open at Login. For more than a handful of Macs, do it properly with a script through Intune.

Ruud’s lesson

A Mac has no C drive, but it does have a place for everything. You just have to stop hunting for letters and start thinking in paths. Ruud now has Shift+Command+G on a sticky note on his monitor, right next to the framed Windows 2000 certificate. “They get along fine,” he says. “Same as on the network.”

Further reading: NAS and network drives on the Mac, a Mac in a Windows network and Outlook, Teams and Microsoft 365 on the Mac.

This is episode 2 of Help, there’s a Mac on my network. Need help with Macs in your organisation? Email frank@analystict.nl.