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Services Utility: Windows Installer Service

Display Name (?): Windows Installer
Short Name (?): MSIServer
Executable (?): msiexec.exe
Library (?): None.
Depends On (?): Remote Procedure Call (RPC)
Supports (?): None.
Description (?): Installs, repairs and removes software according to instructions contained in .MSI files.
OS (?): XP Home/Professional, Vista Home/Business, NT4 Server, 2000 Server, Server 2003, Vista Server
Startup (?):

Explanation (?):

The Windows Installer service is a component built-in to Windows 2000, Windows XP and other newer versions of Windows. It is also available for Windows 95, Windows 98 and Windows NT4 as a service pack addon. In NT based operating sytems (NT4, 2000, XP) this feature is provided as a "run when needed" service.

The purpose of this service is to provide all Windows applications a common means to install programs, uninstall programs, and reconfigure installed options for programs. This means that any program can make use of the API functions provided by the Windows Installer service to elegantly perform these tasks. This has the benefit of the programmers saving time (and money) from not having to recode already written functions. It is more secure because if these programs go through the same installation conduit then they can be controlled by local security options. And it also is more effective and time reliable because in future versions of Windows because the documented installation entry points can be adapted to fit the possibly different operating system structure, thus providing backwards compatability. It also provides the ability to rollback installations, so if an installation is interrupted this service can return your system back to normal without leaving residual damage.

Previously, every program used its own installation means and this was normally accomplished from 3rd party vendors such as InstallShield, but sometimes involved a homebrew installation medium. These external installation programs often created problems by installing outdated / incompatible linked files such as DLLs, and this created unpredictable results that led to system instability. This problem was extremely common in Windows 9x because programs would replace your system files with old Windows 3.x ones and this would create a lot of problems.

The Windows Installer service uses files with the extension of .MSI to perform program installations. These files are compiled scripts that make use of a very powerful backend installation system. Many times these files will come bundled within a programs executable installer.

It should be noted that there are multiple versions of this service available and you may need to upgrade the service to aquire the necessary functionality required by a particular programs installer. Windows XP comes equipped with the newest version called Windows Installer 2.0, but for Windows 2000 you will need to update it. There is supposed to be a newer version released, but the release date hasn't been given.

The Windows Installer service doesn't make me smile. And for every good thing it brought, it also brought a bad thing. One of the worst parts of this service is that it can be damaged and when it is damaged you will not be able to install anything that requires it. Many times a worm will damage this service, and then you're out of luck because you can't install an antivirus scanner. The upside of this is that on all versions besides Windows XP you can uninstall the service and then reinstall it to fix it, but since Windows XP has the latest version this isn't much of a help. Also, this service fails to function in safe mode so you can't remove applications in safe mode that for whatever reason won't uninstall in normal mode, such as they startup and won't shut down to uninstall.

The functionality provided by this service is required for most installations now-a-days. If this service is set to manual then it will start when needed and terminate when finished. If set to automatic the functionality will remain resident and this will provider quicker responses for program installations because it doesn't need to wait for the service to start. If this service is set to disabled then no program that requires the Windows Installer service to install will function properly. For this reason I suggest leaving it set to manual for all types of Windows installations. if you wish to disallow program installations through this service then it would be better if you used group policy to modify its allowances.

Please visit /tools/services/ for the complete Services utility.