What’s the difference between “Macintosh HD” and “Macintosh HD - Data”?

You might have heard of Macintosh HD and Macintosh HD Data, but do you know the difference between them? Fear not, for this article is here to shed light on their distinctions. Keep reading to find out more.

The definition of "Macintosh HD" is the default name given to the primary hard drive on a Mac computer. It refers to the storage device where the operating system, applications, and user files are installed. "Macintosh" is an old term used by Apple to refer to their Mac computers, and "HD" stands for "Hard Drive." This label can be found in the Finder or when booting up the Mac, and it represents the main storage space for the system.

Ever since Apple released macOS 10.15 Catalina, the built-in hard drive on the Mac has been divided into two separate parts. One of them is named Macintosh HD by default.

"Macintosh HD" is mainly used for storing operating system files and applications, hence it's often referred to as the System Volume. Additionally, since "Macintosh HD" contains macOS files, Mac users are not supposed to erase, delete, or modify it freely. Any alteration or deletion of these files could damage the Mac device and prevent it from booting up.

The definition of "Macintosh HD Data" refers to the primary data storage partition on an Apple Macintosh computer's hard drive. "Macintosh HD" is the default name given by macOS to the main volume where the operating system, applications, and user files are installed. The term "Data" in this context typically signifies that it contains the actual user content and system files, separate from any recovery partitions or other volumes that might be present on the same physical hard drive. This partition is essential for the normal functioning of the Mac and holds all the user's documents, settings, and programs.

"Macintosh HD - Data" is another separate partition on a Mac hard drive. This volume is primarily used to store files, such as documents, videos, photos, and audio. Mac users have read and write access to this volume, allowing them to directly edit and manage files on "Macintosh HD - Data."

The difference between "Macintosh HD" and "Macintosh HD - Data"

The main difference between Macintosh HD and Macintosh HD - Data lies in the content they store. The Macintosh HD volume is primarily used for system files and scripts of the Mac, while Macintosh HD - Data serves as the location for storing personal data. Furthermore, the Macintosh HD volume is typically read-only and cannot be modified, whereas users have read and write access to Macintosh HD - Data, allowing for editing operations.

Despite their differences, they have one thing in common: in the Finder, they both appear as a single volume called Macintosh HD.

Which one should I erase, Macintosh HD or Macintosh HD - Data?

We perform different actions on them, so our expectations for the steps involved vary. We'll explain the appropriate steps for each below.

Erase the Macintosh HD volume when reinstalling macOS

Erase Macintosh HD and Macintosh HD - Data for downgrading macOS

Erase the Macintosh HD volume when reinstalling macOS

The Macintosh HD disk volume is your Mac's system volume. As such, it's isolated from all other data. This design is mainly to prevent accidental overwriting of critical operating system files. That's why, when we want to reinstall macOS, we must erase the startup disk in macOS Recovery, which erases the Macintosh HD volume.

Erasing “Macintosh HD” is necessary to create a clean and stable environment for a better macOS reinstall. If you don't erase “Macintosh HD” before installation, errors or failures might occur.

Note: To prevent the loss of important files during a system reinstall, we recommend you back up your crucial data beforehand.

Downgrading to an earlier version of macOS erases both Macintosh HD and Macintosh HD - Data.

Downgrading macOS isn't the same as reinstalling macOS. To downgrade, you'll need to erase both the Macintosh HD volume and the Macintosh HD - Data volume.

When you downgrade macOS, the amount of data from the previous version of macOS is preserved, and the new downgrade creates a new Macintosh HD - Data volume. This causes an issue when a device has two Macintosh HD - Data volumes. Therefore, when downgrading macOS, you need to erase both the Macintosh HD and the Macintosh HD - Data volumes.