How to Reinstall an iMac Restore System

by M.A. Helt

Restoring the system software on an iMac installs a clean copy of the operating system and restores the computer to its initial factory settings. You may need to complete this process if you are encountering software problems or poor computer performance or at the recommendation of an Apple technician. You can restore the system software with or without erasing the entire hard drive. Backing up your computer prior to restoring the software is always recommended, even if you choose not to erase the hard drive.

Erase Hard Drive

Back up the contents of your iMac. Copy all important files to an external hard drive or burn to a CD. Copy all of your documents, photos, music files, e-mail files, Internet favorites and fonts. Do not back up any applications. Instead, locate the installation software for any applications you added to your Mac.

Insert the iMac installation DVD into the computer.

Restart the computer. After you hear the start-up chime, hold down the C key until the menu appears.

Select the language and press the right arrow key.

Select "Disk Utility" from the Utilities menu.

Click the icon of the drive you wish to erase, then select the "Erase" tab at the top of the Disk Utility screen.

Click the Erase tab and accept the warning message. The erase process could take several hours to complete.

Select "Quit Disk Utility" from the Disk Utility menu.

Installing the Operating System

After closing the Disk Utility, you will see the menu for the operating system installation. Click "Continue."

Read the license agreement and click "Agree."

Click the disk where you wish to install the software. The disk icon will turn into a green arrow when selected.

Click "Install" and the process will begin. In some cases, you will be prompted to insert a second disk halfway though the process.

Click "Continue" when a message indicates the operating system has been installed. Then click the "Restart" button.

Mac OS X Setup Assistant

After the restart, the computer will guide you though the Mac OS X Setup Assistant. Begin by selecting your country and clicking "Continue."

Click the icon for your computer keyboard layout and select "Continue."

If you wish to copy information from another computer or your backup drive, select "Migrate Data" and follow the on-screen instructions. If not, select "Do not transfer data."

If you have a wireless Internet network within range, you will see a list of networks. Select the appropriate network and provide the password, if needed, and click "Continue."

Enter your Apple ID, if you have one. Your Apple ID information will be the same as your iTunes account, your MobileMe account or your .mac account. Click "Continue" once you've entered the information. You can also choose not to enter your information and click "Continue."

Mac OS X Setup Assistant, Continued

Fill out your personal contact information on the Registration Page, or choose not to and click "Continue." Your information will be sent to Apple to register your computer if you have an Internet connection.

Enter your computer username and password. You will need to remember this password anytime you need to install software.

Select an icon for your username, or use the built-in camera to take a photo. Click "Continue" once you've selected an icon.

Choose if you would like to set up your MobileMe Account. If you already have an account, enter your log-in information. If you do not have an account, select that option and hit "Continue."

Click "Go" to complete the setup. You will be taken to the desktop of the computer. Eject the installation disk by dragging it to the trash can.


  • You don't always need to erase the hard drive. You can begin this process with Section 2 if you simply need to restore a corrupted operating system, but erasing the drive first will be sure to eliminate any problems.
  • Older iMacs may have two installation CDs, whereas newer iMacs have one installation DVD.

Items you will need

  • Mac OS X Installation CDs or DVD

About the Author

M.A. Helt began writing professionally in 2009 after more than seven years of working in print communications and electronic media for nonprofit organizations and small businesses. In addition to college newspaper writing experience, Helt writes on marketing and technology topics. She holds a Bachelor of Science in graphic and communication design from La Roche College in Pittsburgh, Pennsylvania.