How do I reinstall Mac after replacing hard drive?

Reinstalling your Mac’s operating system after replacing the hard drive can seem daunting, but it’s actually a straightforward process if you follow the right steps. In this comprehensive guide, we’ll walk you through everything you need to know to get your Mac up and running again with a fresh install of macOS.

What You’ll Need

Before starting the reinstall process, make sure you have the following:

  • The new hard drive installed in your Mac
  • A USB flash drive with at least 12GB of available storage
  • A functional Internet connection
  • Apple ID and password
  • Time Machine backup (recommended)

Step 1: Download the macOS Installer

The first step is to download the macOS installer file from the App Store. Here’s how:

  1. On another Mac, open the App Store app and search for your version of macOS, such as “macOS Catalina” or “macOS Big Sur.”
  2. Click the Download button next to macOS. This will download the installer file to your Applications folder.
  3. Once downloaded, quit the App Store.

Step 2: Create a Bootable Installer Drive

With the installer downloaded, next you’ll create a bootable installer drive on your USB flash drive. This will allow you to boot your Mac from the drive and install macOS on the new hard drive. Follow these steps:

  1. Connect your USB flash drive to the Mac you downloaded the installer on.
  2. Open Terminal and type diskutil list to list all drives.
  3. Determine the disk identifier for your flash drive, such as disk2.
  4. Use the following createinstallmedia command in Terminal, replacing [disk#] with your drive’s ID:
    sudo /Applications/Install\ macOS\ [version].app/Contents/Resources/createinstallmedia --volume /Volumes/[disk#] -- /Applications/Install\ macOS\ [version].app
  5. Type your admin password when prompted. This will start creating the bootable installer drive.
  6. When it finishes, you can quit Terminal and eject the drive.

Step 3: Install macOS on the New Hard Drive

With your bootable installer drive ready, it’s time to install macOS on your new hard drive. Follow these instructions:

  1. Connect the installer drive to the Mac with the new hard drive.
  2. Turn on your Mac and immediately hold down the Option key after hearing the startup chime. This will bring up the boot picker.
  3. Select the orange installer USB drive icon and click the up arrow.
  4. When the installer opens, select your language and click Continue.
  5. In the Utilities menu at the top, select Disk Utility.
  6. Click Continue to open Disk Utility.
  7. Select your new hard drive volume and click Erase at the top.
  8. Name the new volume and click Erase to format it.
  9. Close Disk Utility when finished.
  10. Click Install macOS and go through the installation steps to install it on your new hard drive.

Step 4: Migrate Your Data from Time Machine (Optional)

Once macOS is installed, you can optionally migrate your apps, settings, and other data from a Time Machine backup. Here’s how:

  1. When asked if you want to transfer information during setup, select “From a Time Machine backup” and click Continue.
  2. Select your Time Machine drive and backup date.
  3. Click Continue andmacOS will import your data from the backup.
  4. After migration completes, you can finish the rest of the setup process.

Step 5: Reinstall Apps and Settings

If you didn’t migrate from Time Machine, you’ll need to reinstall your apps and customize your settings. Here are some tips:

  • Sign in to the App Store to download your purchased apps.
  • Visit software vendor websites to download and reinstall apps.
  • Manually adjust System Preferences to customize your settings.
  • Sign in to iCloud and other cloud services to sync data.
  • Transfer important files from your backup or old hard drive.

Troubleshooting Tips

If you run into issues during the reinstallation process, here are some troubleshooting tips:

  • Boot to macOS Recovery over the Internet if your USB drive isn’t working.
  • Wipe and reformat the hard drive if the installer can’t recognize it.
  • Use DiskMaker X to create a working USB installer drive.
  • Reset NVRAM if your Mac gets stuck during the boot process.
  • Use Target Disk Mode to connect your Mac to another one.

Frequently Asked Questions

Do I need to back up my Mac before replacing the hard drive?

Yes, it’s crucial to have a full backup before replacing your hard drive. The best option is Time Machine as it allows easy restore during setup. Alternatively, you can use cloud backup services or clone your current drive.

Can I install an older version of macOS on a new hard drive?

No, Apple does not allow installing older macOS versions than what came with your Mac model originally. You can only install the version your Mac shipped with or newer.

How do I get software and drivers after reinstalling macOS?

You’ll need to manually reinstall third-party apps, drivers, and utilities from the vendor websites after the OS reinstall. Check the vendor support sites for the latest versions compatible with your macOS version.

Is it better to erase and install or upgrade when replacing a hard drive?

It’s generally better to erase your new drive and do a clean install of macOS rather than attempting an upgrade install. Upgrades can carry over old files and settings that may cause issues.

Can I reuse my old Mac hard drive as an external drive?

Yes, you can insert your old Mac hard drive into an external enclosure to use it as an external drive after replacing it. This allows you to access your old files and backups.


Reinstalling macOS on a new hard drive involves creating an installer drive, erasing and formatting the new drive, installing the OS, and finally migrating data from backup. Be sure to have a current backup before replacing your drive. With some time and patience, you’ll have your Mac running smoothly again with your files and settings intact after replacing the hard drive.

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