The concept of user accounts is central to OS X’s security approach. Like the Unix under its skin (and also like recent versions of Windows), OS X is designed from the ground up to be a multiple-user operating system. That is, you can set up your OS X so that everyone must log in—click his name and type his password—when the computer turns on (Figure 13-1).
Upon doing so, you discover the Macintosh universe just as you left it, including these elements:
Your documents, files, and folders.
Your preference settings in every program you use: Web browser bookmarks and preferred home page; desktop picture, screen saver, and language; icons on the desktop and in the Dock—and the size and position of the Dock itself; and so on.
Email account(s), including personal information and mailboxes.
Your personally installed programs and fonts.
Your choice of programs that launch automatically at startup.
This system lets different people use it throughout the day, without disrupting one another’s files and settings. It also protects the Mac from getting fouled up by mischievous (or bumbling) students, employees, and hackers.
Figure 13-1. When you set up several accounts, you don’t turn on the Mac so much as sign into it. A command in the menu called Log Out summons this sign-in screen, ...