OS X El Capitan arrived on 30 September. If you want to try out Mac OS X 10.10 El Capitan before going the whole hog and installing it on your Mac, you might want to consider dual-booting the El Capitan beta alongside your current edition of Mac OS X 10.10 Yosemite.

This method is particularly pertinant for those who installed the public beta of El Capitan. We advised people taking part in the beta program to be very careful when installing the public beta of Mac OS X 10.11 because by its nature beta software can introduce bugs and performance problems, important apps and programs may not work, for example. Moreover, you might find it crashes and is unstable in a way you may not be used to from Apple products. By the time the new version of OS X launched on 30 September these issues should have been ironed out, although as expected there were still problems (Office 2016 and the Apple Mail app were negatively affected).

This feature looks at ways for you to install Mac OS X 10.11 El Capitan without having to remove your Mac OS X 10.10 Yosemite installation. With a dual-boot installation, you are able to choose between using Mac OS X 10.10 Yosemite or Mac OS X 10.11 El Capitan.

This could be useful if you are a beta tester of El Capitan still looking at the various updates to the operating system.

See also: How to make a bootable OS X 10.10 Yosemite install drive | How to update to the new Mac software, how to download OS X El Capitan |Top tips for OS X El Capitan

Dual boot El Capitan on a second hard drive

The easiest way to install Mac OS X 10.11 El Capitan if you want to be able to keep your Yosemite installation as it was, is to place it onto a second hard drive. This second drive can be either an internal hard drive (if you own an old model Mac Pro with multiple hard drive bays, or have installed a second hard drive in an older MacBook Pro) or an external hard drive.

The external drive is a good option, however, because the speed of the new Thunderbolt drives is largely comparable to the internal drives on a Mac. If you do not have a Mac with Thunderbolt then consider using a USB 3.0 drive.

Adding a second hard drive, formatting it and installing Mac OS X 10.11 El Capitan on it is probably the simplest way to get a good look at the new operating system. It'll leave your current configuration intact and allow you to play around with Mac OS X El Capitan before you commit to the full install.

See also: Run Windows on Mac: how to install and run Windows | How to dual boot a Mac with Windows and OS X | How to partiton your Mac

How to install El Capitan on an external hard drive

How to erase an external hard drive

If you've got a spare external hard drive that you want to dedicate to Mac OS X El Capitan, then this is a good way to go about it (note that this erases the drive):

  1. Connect the external hard drive.
  2. Launch Disk Utility (choose Go > Utilities to find it).
  3. Select the drive in the sidebar (the root drive, not the volume it contains).
  4. Click Partition.
  5. Ensure that Partition Layout says 1 Partition.
  6. Give it a name like "Mac OS X El Capitan".
  7. Click Options and ensure that Guid Partition Table is selected. Click OK.
  8. Click Apply and Partition

(Note these images are of a Yosemite installation on a separate drive, but the same applies for El Capitan)

Check that the external hard drive Option states GUID Partition Table

Now download El Capitan from the App Store - it will be available from 30 September.

Install Mac OS X on to the external drive

Follow these instructions:

  1. Open the Install OS X 10.11 Developer Preview file in the Applications folder.
  2. Click Continue.
  3. Click Agree and Agree.
  4. Click Show All Disks.
  5. Highlight the external hard drive.
  6. Click Install.
  7. Enter your Admin password

The Mac reboots, and you go through the installation process as normal, but El Capitan is installed on the external hard drive.

Choose between Mac OS X 10.10 and 10.11 by opening System Preferences > Startup Disk. Select the drive you wish to start up the Mac and click Restart. You can also hold down Option during startup to pick the drive you wish to use to start up the Mac.

Dual boot El Capitan by partitioning your Mac

If you want to have El Capitan on your computer rather than a second drive, there is one option, which is to partition the main hard drive into two separate drives and then install Mac OS X 10.10 Yosemite on one-partition and El Capitan on the other. Read how to run El Capitan and Yosemite side by side on your Mac here.

This Apple Support document has more information here about partitioning your main hard drive.

Dual boot Yosemite and El Capitan using virtualisation software

The final option is to install Mac OS X10.11 El Capitan inside Mac OS X 10.10 using virtualisation software such as Parallels Desktop or Fusion. The virtual route enables you to try out Mac OS X in a safe environment without affecting your Mac OS X 10.10 Yosemite installation.

You can also read about using virtualisation software to run El Capitan here.

Here are our top ten features coming in OS X El Capitan and How El Capitan compares to Yosemite

If you install El Capitan and then think you made a mistake, here's How to remove El Capitan and revert to Yosemite

Read next: Features in OS X 10.12, successor to El Capitan: Wishlist