From Mavericks to Snow Lion: how to get back? I upgraded from Snow Lion to Mavericks and just found out that I can't sync my address book and calendar between my iMac and iPhone (3GS) using iTunes. I'm not using iCloud and not willing to use it either. All my data files (from Mail etc.) are also "upgraded" to Mavericks. Is it possible to reinstall Snow Lion and use Time Machine to place all date files back or am I going to be in trouble here?

Added: I meant Mountain Lion (in stead of Snow Lion -- sorry ;-))
There is no "Snow Lion"—Snow Leopard, Lion, and Mountain Lion strike me as possibilities—but regardless, the answer is the same: you can roll back with your Time Machine to an earlier version of OS X:


Enter Recovery by rebooting and holding command+R.
Select "Restore from a Time Machine backup".
Select a backup from before your Mavericks upgrade.


Unfortunately, you may not be able to use all of today's data from a pre-Mavericks installation.  Some Mavericks applications (such as Mail.app) will upgrade their databases.  That data will not be able to be understood by pre-Mavericks versions of those applications.  If you haven't had any significant data changes since your upgrade, I would recommend a wholesale reversion back to your preferred OS.  If you have, perhaps you could roll back anyway and copy newer files from your Time Machine individually, provided they are not in a format your old OS can understand.

Apple TS article: OS X Mavericks: Revert to a previous OS X version