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Display Name (?):

Fast User Switching Compatibility

Short Name (?):

FastUserSwitchingCompatibility

Executable (?):

svchost.exe

Library (?):

shsvcs.dll

Depends On (?):

Terminal Services

Supports (?):

None.

Description (?):

Provides management for applications that require assistance in a multiple user environment.

OS (?):

XP Home/Professional, Vista Home/Business

Startup (?):

Default	Home	Workstation	Server	Minimal	Tweaked	Automatic
Manual	Automatic	Manual	Manual	Manual	Disabled	Automatic

Explanation (?):

The fast user switching compatibility service is referenced when a user attempts to execute an application when it is already in use by another user on the system. This situation arises from using the fast user switching feature of Windows XP (and above) that allows you to logoff your computer without closing your applications so you can resume where you left off when you log back in. When using fast user switching any applications that are left open when you log out remain active even when someone else logs into the computer. This is especially useful in a family environment. This service is a hack that allows for programs that weren't originally designed for fast user switching to run without creating problems. The general purpose is to bypass the problem that an application would have from being launched twice. If an application that wasn't designed for faster user switching is opened and locked by one user, then if another application attempts to access this program there could be a problem with the application executing properly a second time.

As such this service will perform one of four possible actions if a problematic situation occurs in which a file lock is interferring with the execution of a shared application. (1) The first is that if the user possesses administrative rights the application in question will be terminated by the inactive user and executed by the active. If the user does not possess administrative rights the user will receive an error that the application cannot be opened without the inactive user closing their inuse program. (2) The second is that whenever a user is switched or the computer is returned to the fast user login screen any program that would have issues with fast user switching would be closed. (3) The third is for any program that uses resources such as serial ports, which cannot be shared. In this case the program will be closed when inactive and reexecuted when active. (4) The fourth case is similiar to the second action, but the only difference is that the application is terminated only when the user is switched and not when returning to the welcome screen. This applies mainly to applications like media players. To see what application has what mode assigned to it install \Support\Tools\Act20.exe from your XP CD and run the Compatibility Administration Tool. Under compatibility fixes there will be FUSBadApplicationTypeX (where X is the action type).

On a computer that is not shared you may safely disable (or better yet, set it to manual) this service as well as the fast user switching ability (the feature itself is found on the User Accounts screen in the Control Panel. However, even with fast user switching on this service is not required as it only increases the functionality of the feature. In a corporate environment this service should definitely be disabled. For a computer that is shared by several people and has enough memory to support each instance of someone logged in then this feature could definitely be useful, and if you have fast user switching enabled it is highly suggested to use it in conjunction with this service as it reduces problems that may appear.