Using Older Version of Mac OS X [ Good or Bad ] ?

Your Mac is designed to work with compatible versions and builds of OS X. If you try to use a version or build of OS X that's not compatible with your Mac, your computer might behave unexpectedly.

Avoid using versions of OS X that are older than what came with your Mac.

If you copy older system files from another computer to your Mac, or try to use startup disks designed for older computers, you might see one or more of the following:

• Your Mac doesn't start up, or you see a prohibitory symbol at startup
• You see a message that you're using an unsupported or incorrect version of OS X
• Your Mac doesn't respond to your trackpad, mouse, or keyboard
• Apps unexpectedly quit
• Your Mac doesn't sleep or wake
• You don't hear any sound from your Mac
• The fans in your Mac operate at a faster or louder speed
• The image on your display appears to "shrink" or has black bars around it, or appears tinted
• You can't use Bluetooth or Wi-Fi

If you need to reinstall OS X, use OS X Recovery. You can also use the Mac App Store to install newer versions of OS X that are compatible with your Mac.