Backing up OS X
Does backup to Time Machine automatically backup OS X?
MacBook Pro 13″, OS X 10.10
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Time Machine in its default mode will backup everything on your mac or attached to your mac, including the OS.
If you open System Preferences> Time Machine> Options in that you add items files, folders, disks etc to be excluded
from the backup. Use the + and - buttons to add or remove items at your discretion.