OS X Yosemite Partition from El Cap

[afsnyder]

How do I install OS X Yosemite on another partition from OS El Capitan DP2? I downloaded the App Store installer app but it doesn't open on El Capitan. What are my options?

 

[KALLT]

Put it on a thumb drive and boot from it. Alternatively, use Internet recovery (command + option + R on boot) to install the OS that was shipped with your Mac and then upgrade to Yosemite from there.

 

[AppleFan22]

How do I install OS X Yosemite on another partition from OS El Capitan DP2? I downloaded the App Store installer app but it doesn't open on El Capitan. What are my options?

After you get Yosemite running, I'll assume you'd want to have it as a partition in your hard drive, yes? Create a small back up of Yosemite, create a partition of your hard drive, boot into recovery mode, and then go to the Time Machine pane. From there, you can have it install Yosemite into your new partition.

I don't quite know how the thumb drive idea (above) works, but once you get Yosemite running, this method will finish it off for you.