Windows Installer Technology

Windows 2000 (Win2K) contains a set of new Change and Configuration Management (CCM) technology features known as IntelliMirror. Using IntelliMirror, you can configure data and applications to follow clients around a network, centrally define client desktop settings for computers and users, and centrally deploy Windows 2000 Professional (Win2K Pro) on desktops using Remote Installation Services (RIS).

One important part of IntelliMirror and a core component of Win2K’s CCM technology is Windows Installer. Using Win2K, administrators can control user file systems and Registry entries and approve the applications that users can install on their computers. Such applications run as the local system account on client desktops. Because these users are installing the applications with an elevated privilege, they don't need high-level (e.g., Administrator) privileges.

What Is Windows Installer?
Windows Installer is a service that's responsible for managing installation processes under Win2K. Windows Installer uses the .msi file format, which replaces the setup program (typically setup.exe) that you have used for years to install software.

Windows Installer technology consists of two parts:

• The .msi package file
• The msiexec.exe installer program that runs on the client side

The .msi package file contains a relational database of information that stores instructions for installing and removing applications. When you make modifications to one of the database's tables, the changes automatically propagate across the database because of its relational nature.

Msiexec.exe uses a dynamic link library (DLL) called msi.dll to read the .msi package file. The program copies files to the hard disk, creates shortcuts, modifies Registry entries, and performs other tasks. How does the system know that .msi files are executables? When you install Windows Installer on your computer, Win2K automatically configures the file association so that .msi files associate with Windows Installer and the system runs msiexec.exe, as Screen 1 shows.

You can use Windows Installer to install software locally. You can also use the tool with Systems Management Server (SMS) to centrally deploy software. Windows Installer offers self-healing and resiliency to Win2K desktops—corrupted software can repair itself and deleted applications can automatically reinstall.

Installing and Removing Applications
With Windows Installer, you can install and uninstall applications without affecting the system state or harming other applications. The tool is smart in that it keeps track of all the modifications it makes to the system during the software installation. If your installation crashes, Windows Installer will roll your system back to its original state.

Windows Installer uninstalls applications properly, removing Registry entries and deleting application files without harming the shared files that other applications use. You can right-click a Windows Installer package (an .msi file) in Windows Explorer and select Install, Repair, or Uninstall. Alternatively, you can use the Control Panel’s Add/Remove Programs applet to change or remove a Windows Installer package.

Detect and Repair
Applications can ask Windows Installer to determine whether any program files are damaged or missing. If so, the tool can repair a program by replacing corrupted or missing files. To repair missing files and correct Registry entry problems, choose Detect and Repair from an application’s Help menu. Screen 2 shows Microsoft Excel 2000's Detect and Repair dialog box.

You can also have Windows Installer restore program shortcuts to the Start menu by selecting "Restore my shortcuts while repairing," as Screen 2 shows. When you click Start, Windows Installer detects and repairs damaged Microsoft Office 2000 installations. Windows Installer can’t repair your personal data files; it can repair only software that it installed.

Advertising
If you’ve installed Microsoft Office 2000, you’re already familiar with another feature of Windows Installer—Advertising. Advertising is a feature that lets you install a small subset of applications initially and have additional components install automatically when you use them for the first time. Windows Installer can also remove components that you haven't used for a while. For example, you can configure the tool to remove Microsoft Word's mail merge feature if you haven't used it for 30 days.

Windows Installer is a powerful tool that's much more than just an installation wizard. It's an extensible software management system that supports software installation from multiple sources. Third parties and developers can customize Windows Installer to best suit their needs.

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