MSI

MSI files are database files, used by Windows Installer. They contain information about an application which is devided into features and components, and every component may hold files, registry data, shortcuts etc. The MSI file also contains the UI that is to be used for installing, and various other data such as any prerequisites to look for, custom actions to execute, the order of the installation procedure, whether to support Administrative installations, etc. It can also contain the actual files to be installed themselves (this isn't always the case though, the files can also be in an external CAB file or just as plain uncompressed files in a location where MSI can find them). MSI files are the current recommended way of doing installations on Windows. The alternative is writing a program that performs the installation itself. MSI files are executed by an EXE file that is part of Windows, called MSIEXEC.EXE. This application reads the data in the MSI file and executes the installation.