Most of the time you'll never have to worry about having to install a new operating system on your Mac - the one that's on there should work fine through thick and thin. But every once in a while you might want or need to - here are step by step instructions for making it happen.

Use Recovery Mode

Every Mac operating system since Lion (OS X 10.7) has included Recovery Mode, a special boot partition that enables you to recover from catastrophic failures and problems. This can be used to install a fresh copy of Mavericks on your hard drive, provided you have Internet access. To use Recovery Mode, follow these instructions:

  1. Shut down your Mac.
  2. Press the Power button (the button marked with a O with a 1 through it)
  3. Immediately press the command (cloverleaf) key and R together.
  4. Make sure you're connected to the internet through Wi-Fi. If you're not, choose a network from the Wi-Fi menu that appears at the top-right corner of the screen.
  5. Select Install Mac OS X, then click Continue.
  6. Wait.

It's worth noting that this installs a fresh copy of OS X on your Mac without affecting either your files or your user settings, so you should be good to go as soon as it reboots. All applications are maintained, as well. This system simply replaces the core files that enable OS X to operate.

I've had occasion to see systems that don't work with Recovery Mode, for some reason. For those computers, it's often possible to restore access to the Recovery Mode partition by resetting the System Management Controller (SMC). To reset the SMC on most Macs:

  1. Shut down the Mac. If it's a laptop, make sure it's connected to the power cord.
  2. Hold down the Control, Option, and Left Shift keys simultaneously, then press the Power button.
  3. Release the keys.
  4. Press the Power button again. The system should turn on and you can give Recovery Mode another try.

If that fails to work, you can always download a fresh copy of the Mavericks installer from the Mac App Store.

Download a fresh copy of Mavericks from the Mac App Store

  1. Open the Mac App Store application, either from your Dock or from the Applications folder.
  2. Click on the Purchases tab at the top of the window or press command and 4 on your keyboard. (I'll assume for the moment that you have already installed Mavericks once - if you haven't, you should see an installation option in your Updates folder, assuming you have Snow Leopard or later installed.)
  3. Find OS X Mavericks in the list of files, either scrolling through the list or using the Search field in the upper right hand corner of the window.
  4. Click the Download button.
  5. You may get a dialog box advising you that OS X 10.9 is already installed on this computer. It's safe to click the Continue button.
  6. Be prepared to wait a while. Even over a fast Internet connection, it'll take a little while to download, since it's more than 5 GB.
  7. Once it's downloaded, it'll launch automatically. Follow the directions to install OS X.

Hopefully this will help you get started if you need to install a fresh copy of Mavericks. Questions? Fire away in the comments.