Select “El Capitan” (or whatever the drive partition you created was named) and choose “Install”, let the installation finish and the Mac will reboot automatically into OS X El Capitan when done.Launch the “Install OS X El Capitan” application, agree to the TOS, and when the drive selector shows up, click on “Show All Disks”.Click on “Apply” to create the new partition, and confirm when requested that you wish to partition the target volume, let the partition finish creating then quit out of Disk Utility.

Click the plus button to create a new disk partition on this volume, give it an obvious name like “El Capitan” and resize it accordingly.

Open Disk Utility and select the hard drive you wish to partition from the left side menu (often called “Macintosh HD”.

Creating a New Partition & Installing OS X El Capitan to Dual Boot the Mac By the way, if you are using a bootable installer drive, you can perform this partitioning process directly from there. We’ll partition the drive, then install OS X El Capitan onto that new partition. So you backed up and meet all the requirements, you’re ready to go.

Finally, you’ll want to be certain the Mac can run OS X El Capitan, the system requirements are fairly forgiving but double-check anyway.The OS X El Capitan installer, whether that’s running directly from the /Applicaitons/ folder as downloaded from Apple, or already made into a bootable El Capitan installer drive does not matter, either will work just fine.Back up the Mac with Time Machine, do not skip this, partitioning a Mac and installing new operating systems has some degree of risk and you do not want to be in a situation where you incur permanent data loss simply because you did not back up.Sufficient hard disk space available to partition the drive in question, and install OS X El Capitan onto that new partition (at least 40GB free is recommended, with a minimum of 20GB for El Cap – do not let either Mac OS X install run too low on available disk space as performance will greatly suffer).Before beginning, you will need the following:

Install os x el capitan to new drive