- 1). Insert the Mac OS (operating system) Installation Disc (the one that came with your computer, or, if you have since upgraded to a new OS, the newest installation disc you have) into your external CD-ROM. Then, insert the USB plug into your computer.
- 2). Double-click the disc icon, which will appear as "Install Mac OS X" on your desktop. (If you are installing the OS Leopard, your computer will prompt you to restart; if you are installing the OS Snow Leopard, you do not need to restart your computer.) Click "continue" after the first pop-up window. (If you are installing Snow Leopard, you will need to read the license agreement and click "agree.")
- 3). Select the disk you want to install the operating system to, which will most likely be your computer's internal hard drive (and by default labeled "Macintosh HD"). Then click "continue."
- 4). Click "install" and wait. This process may take a few hours. The computer will prompt you to restart once it is finished.
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