All Macs with OS X Mavericks, Yosemite, Lion, Mountain Lion, have a bootable Recovery partition that can be accessed in case of system problems, allowing you to troubleshoot, restore from Time Mach…
How to Boot into Recovery HD Partition on a Mac OS X with Yosemite, Mavericks, & Mountain Lion
OS X Yosemite on Unsupported Macs [Guide], Page 41
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