A. Fast User Switching is an XP feature that lets more than one user simultaneously log on, although only one user account can be active at any time. For example, say user John is currently logged on and Kevin needs to print a document from his desktop. Without logging off John, Kevin can log on, print his document, then make John's user account active again without logging off to perform the switch.

Several factors determine whether Fast User Switching is available:

  • You must not be using a third-party Microsoft Graphical Identification and Authentication (msgina.dll) file.
  • The computer must not be a member of a domain (this factor applies to XP Professional only).
  • You must enable the Fast User Switching feature (go to Start, Settings, Control Panel, User Accounts, and select "Change the way users log on or off"). If the computer has more than 64MB of RAM, XP enables Fast User Switching by default.
  • The computer has sufficient free resources to create an additional Winlogon service thread (when multiple users are logged on, all the accounts--even those note currently in use--use resources).
  • If your computer video card uses Shared Video Memory (i.e., the computer uses a portion of the system's RAM for video display memory), the shared memory will minimize the amount of free RAM and can cause XP to disable Fast User Switching.