In the course of using a computer, you will come across a variety of file extensions that indicate various purposes for that file. One such extension is ".msi," which is used by Windows to install software.
"MSI" stands for "Microsoft Installer." The extension ".msi" describes a standardized installation system that is now referred to as "Windows Installer," but the extension name has not been changed.
Windows allows for a wide variety of installer types. The advantage of using its official MSI platform is that it provides a more predictable and reliable method for installing, managing and un-installing Windows programs.
There are five major versions of MSI. Version 4.0 arrived with Windows Vista and allows for installations that do not require administrator privileges (as in having to enter the system password to install the program).
The fifth version of MSI arrived with Windows 7. This version allows more settings for compatibility mode (when you're trying to install a program designed for an older version of Windows).
MSI and Other Operating Systems
MSI files cannot usually be installed in OS X or Linux. However, a program called Wine can give those users a varying degree of success by acting as a sort of translator.