When you initially setup a new Mac you'll run through a program called Setup Assistant to create the initial account on your Mac known as the Administrator.  After this step, you'll then be logged into your Mac.
Macs with only one Account
If you are the only user on your Mac you have the option to configure Mac OS X to ask for login credentials otherwise by default your Mac will log anyone into your account when they turn on your Mac.  It is recommended that you enable a quick and easy to configure security feature that will disable automatic logins

  1. Launch System Preferences
  2. Click Security

    system_preferences_security_01.png
  3. Enable the checkbox next to "Disable automatic login"

    security_disable_autologin_01.png
The next time you turn on your Mac you'll be asked to enter your account password.  Imagine if you didn't implement this very simple lock down and your Mac was stolen.  Anyone would be able to access your files and anything stored on the hard drive and/or your MobileMe iDisk.

Macs with more than one account
A Mac with multiple accounts is recommended, even if you are the only user.  The moment you have setup more than one account and power up your Mac, you (or anyone who turns on your Mac) will presented with the Mac OS X Login Screen even if the "Disable automatic login" feature has not been enabled in System Preferences.

If Fast User Switching is Enabled
fast_user_switching_menulet_01.pngFast User Switching is a feature that can be enabled for Macs with multiple user accounts that allows one user to log in without requiring another user to log out.  If enabled, the Fast User menulet will be visible.
  • Click on the Fast User Switching menulet as shown at the upper right
  • Select another user
Mac OS X will then log into that other account after the password has been entered.  Any previous account will remain running in the background preserving the state it was last in.  Note that only one user's Desktop will be visible at a time.

Updates
  • March 15, 2009 - content revision, image updates
Created: 12:21 PM on Dec 29, 2006
By: switchtoamac