Learn the system requirements for OS X Mountain Lion.
Learn about the system requirements for OS X Mavericks.
The Wake on Demand feature of Mac OS X v10.6 or later, lets your Mac continue to share items (such as music, printers, files, or your screen) when it is asleep.
If you want to switch to a different TIme Machine backup drive, use this article to learn how to transfer your existing Time Machine backups to the new backup drive, and then use it for regular Time Machine backups.
Learn how to reset (flush) the DNS cache.