What is the Windows Installer (MSI) engine? It's the part of the Windows that handles installations. It was introduced in Windows 2000, though there are upgrades for earlier versions of Windows. You probably have it as the MSI engine ships with all current Windows operating systems. The Zillions installer uses version 2.0 and older systems may not have this. Installation of the the MSI engine requires a reboot. Otherwise, the installer won't reboot. The MSI 2.0 engine may also be downloaded and from Microsoft's site and installed separately.