This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
This has been asked and answered exhaustively many, many times. Please use the "Search" link at the top of the page to find the previous discussions. Make sure you search through all forums, not just this one.