Apple made available the public beta version of OS X Yosemite to not only registered account but everyone else interested to test the Mac OS X. For others, it is now possible to retrieve a code directly on the page reserved for this purpose. In order to proceed, you have first sign in using your Apple ID on the OS X Beta Program.
Dual booting means that the computer installed two operating systems, and when you start the user selects one of them. OS X 10.10 Yosemite will operate independently from the main system OS X 10.9 (or even 10.8, 10.7 or 10.6, if you have an older Mac) with their parameters and established programs.. Before proceeding to the breakdown of the hard drive into sections, be sure to make a backup copy of your files.
Dual-boot OS X Yosemite and OS X Mavericks:
Step 1: Download the OS X Yosemite beta version from https://appleseed.apple.com/sp/betaprogram/
Step 2: When completed, open Disk Utility from the Applications folder -> Utilities.
Step 3: Select the main Mac hard drive from the sidebar, then click the disk partition.
Step 4: Click the “+” next to the partition layout. Take the new OS for at least 15 GB and name the new partition OS X Yosemite. Click Apply.
Step 5: After completing the operation close the Disk Utility, and then run the installation file «Install OS X 10.10 Developer Preview” Applications folder.
Step 6: In the setup menu, choose the OS X Yosemite as the main drive (you have to use the command “Show all drives” to see the partition).
Installs Mac OS X Yosemite and launch a new Os X 10.10 and to go back the previous OS,, restart the computer while holding (Alt), and select the boot menu OS X Mavericks.