History of macOS and macOS File Structure

Early Apple Days

Apple was established on April 1, 1976, and quickly made its mark with the Lisa in the early 1980s, the first public computer featuring a graphical user interface (GUI). Fast forward to 1984, and Apple released the Macintosh, their first affordable personal computer with a GUI, revolutionizing personal computing.

Big Moves in the 1990s and Beyond

By the late 1990s, Apple was well-established. In 1998, they introduced the HFS+ file system, which helped users manage larger storage devices and improved overall file organization. But things really got interesting in 2001 with the launch of macOS X—a Unix-based operating system that gave the Mac the robustness and reliability it needed.

The Evolution of macOS

• 2012: With OS X 10.8 (Mountain Lion), Apple started to unify its desktop and mobile platforms, borrowing elements from iOS.

• 2016: Apple rebranded OS X to macOS, beginning with macOS 10.12 (Sierra).

• 2017: The APFS file system (Apple File System) was introduced to replace HFS+, designed to be faster and more efficient, especially for SSDs.

APFS: Apple's Modern File System

When Apple introduced APFS in 2017, it addressed many limitations of its predecessor, HFS+. Here’s what makes APFS special and why it matters for modern Macs:

• Optimized for SSDs: APFS is designed to work seamlessly with solid-state drives (SSDs) and flash storage, making your Mac much faster when it comes to file operations.

• Atomic Safe Save: Ever worried about losing data if your Mac crashes while saving a file? APFS uses a technique called Atomic Safe Save. Instead of overwriting files (which can corrupt data during a crash), it creates a new file and updates pointers—meaning your data is much safer.

• Full Disk Encryption: APFS builds encryption right into the file system, giving you multiple ways to secure your data using different recovery keys, including your password or even iCloud.

• Snapshots: One of the coolest features is snapshots, which create a read-only copy of your system at a specific point in time. If something goes wrong, you can roll back to a previous state—perfect for troubleshooting!

• Large File Capacity: APFS supports filenames with up to 255 characters and file sizes up to a theoretical limit of 8 exabytes (that’s 8 billion gigabytes!). So, you probably won’t run out of space anytime soon.

• Accurate Timestamps: With nanosecond accuracy, APFS records changes precisely—useful for backups, file versioning, and tracking down when exactly something was altered.

macOS File Structure: How Your Files Are Organized

macOS organizes files and folders into four main domains, each serving different purposes:

1. User Domain (/Users)

This is where all the files related to your user account live. It includes the home directory, which stores personal documents, downloads, music, and more. Each user on the system has their own isolated space here. There’s also a hidden Library folder within each user account, where your apps store personal preferences and data.

Key folders in the User Domain:

• Home Directory: Your personal space, with folders like Documents, Downloads, and Desktop.

• Public Directory: A space where you can share files with others who use the same Mac.

• User Library: Hidden by default, but this folder is a treasure trove for advanced users and app developers. It contains your preferences, app data, and cached files. If you ever need to dig in, you can reveal it using a simple Terminal command:

chflags nohidden /Users/<username>/Library

2. Local Domain (/Library)

This domain contains files and apps that are shared across all users on the Mac.

Apps installed via the Mac App Store will be located in the /Applications folder. There’s also a /Developer folder here if you’ve installed Xcode or developer tools.

/Library – Library files shared across all users.

3. Network Domain (/Network)

The Network Domain is for shared resources like network drives or printers. In an office setting, this is where you’d find shared servers or Windows file shares. It’s managed by network administrators and isn’t something the average user interacts with often.

4. System Domain (/System)

This is where Apple stores the critical components that make macOS run smoothly. It’s locked down so that regular users can’t accidentally delete something important. You’ll find OS-level libraries and apps here, safely tucked away from tampering.

A Deeper Look into the User Domain

The User Domain is often the center of attention during troubleshooting or security incidents. Whether it's a malicious app trying to access personal files or suspicious activity in the system, the User Domain holds a lot of valuable evidence. It's divided into three main directories:

1. Home Directory

Your personal space for files like downloads, documents, music, and more. Each user on the Mac has their own home directory, and macOS prevents other users from accessing it unless they have special permissions.

2. Public Directory

This folder is for sharing files with other users on the same Mac. It’s located at

 /Users/<username>/Public.

3. User Library

Hidden by default, the User Library stores a lot of important app data. It contains application sandboxes, preferences, and cached data—things you wouldn’t normally touch but are critical to how apps function.

• Application Sandboxes: Found in ~/Library/Containers, this is where macOS keeps app data safe and separate from the rest of your system.

  
  

(i) ~/Library/Containers for data relating to specific apps

(ii) ~/Library/Group\ Containers/ for shared data.

(iii) ~/Library/Application\ Support/ folder and you should always check both to find all the data for a specific application.

• Preferences: Stored in ~/Library/Preferences, these files keep track of how you like your apps set up. For example, the Safari browser’s preferences are in com.apple.Safari.plist.

• Cached Data: Found in ~/Library/Caches, this folder holds temporary files that apps use to speed things up.

  
  

Final Thoughts

macOS and its APFS file system are designed to provide a smooth and efficient experience, especially on modern hardware. The system balances speed, security, and reliability with features like snapshots, encryption, and safe saving methods. By organizing files into distinct domains (User, Local, Network, System), macOS ensures that both individual users and administrators have easy access to what they need while keeping everything secure.

Akash Patel