OS X El Capitan supports two methods of installation. The default method is an , which will upgrade your Mac to El Capitan while preserving all of your user data and. This is the most common means of upgrading the operating system and is recommended when your Mac is in good shape and having no problems. The other installation process is known as the clean install. It replaces the contents of a selected volume with a new, pristine version of OS X El Capitan that does not include any previous versions of the , applications, or data files that may have been present on the selected drive. The clean install method is a good choice for testing a new OS on a dedicated drive or partition, or when you have been experiencing software related issues with your Mac that you have not been able to fix. When the problems are severe enough you may be willing to trade keeping all of your apps and data for starting with a clean slate. If you're going to install OS X El Capitan on your current startup drive using the clean install method, then you will by definition erase everything on the startup drive as part of the process. No matter why you're undertaking a clean install, you should have a current backup of the existing startup drive's contents. You can use to perform this backup, or one of the many cloning apps, such as , , or ; you can even use. The choice is up to you, but whatever you choose, it's important to take the time to create a current backup before you start the installation. Types of Clean Installs Clean Install on Startup Volume: The second option, and perhaps the more common of the two, is to perform a clean install on the current. Because the clean install process erases the contents of the destination drive, it's obvious that you can't boot from the startup drive and then try to erase it. The result, if it were possible,. More than likely it's already connected to your Mac, but if it isn't, you can connect it now. This should include the bootable USB flash drive you just created. Use your Mac's arrow keys to select the OS X El Capitan installer on the USB flash drive, and then press the enter or return key. This can take a bit of time, depending on the speed of the flash drive as well as the speed of your USB ports. This can include all your user data, music, movies, and pictures, as well as the current version of OS X installed. Make sure you have a current backup before proceeding. This will likely be in the Internal category, and may be named Macintosh HD if you never renamed the startup drive. You can leave the name the same, or enter a new one. Make sure that OS X Extended Journaled is selected, and then click the Erase button. Once the process is complete, you can quit Disk Utility. At this point in the clean install of OS X El Capitan, the two supported methods of performing a clean install are about to merge. If you chose to perform a clean install on your current startup drive, as defined in the beginning of this guide, you then performed all of the tasks on Step 1 and have erased your startup drive and started up the installer. Read through the terms and conditions, and then click the Agree button. Click the Agree button. If it is correct, you can click the Install button and skip ahead to Step 6; otherwise, click the Show All Disks button. The time estimate isn't very accurate, so this is a good time to take a coffee break or go for a walk with your dog. Make your selection from the list, and click the Continue button. Make your selection, and click Continue. Here you can choose to move existing data from a Mac, PC, or Time Machine backup to the clean install of OS X El Capitan. You chose a clean installation for a reason, including the possibility that you were having issues with your previous installation of OS X. Before you bring data over, it's a good idea to make sure your Mac operates without issue with a clean install first. Make your selection, and click Continue. Enabling this service will generally allow apps to see where your Mac is located geographically. Some apps, such as Find My Mac, require Location Services to be turned on. However, since you can enable this service later from the System Preferences, I recommend not enabling the service now. Make yo
