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Everything You Need to Know (But Don't) About the MSI File Format

Everything You Need to Know About MSI File Format
Everyone knows that files that have a .MSI extension have something to do with program installation, but have no knowledge about them. We, at Techspirited, have put together a small guide that will answer all the questions you have ever had about MSI format files.
Padmini Krishna
Last Updated: Apr 9, 2018
A Brief Glance...
The extension .MSI comes from Microsoft Installer, which is what the Windows Installer program was called earlier. A file with this extension contains all the required data, ranging from registry entries and shortcuts to the UI of the installer itself. The file can be used to install, delete, modify, or troubleshoot any application program.
As the regular use of computers has become an inherent part of our lifestyle, we frequently encounter files with extensions such as .MSI, .EXE, and so on. Although, we never give it a conscious thought, the urge to know more about it, remains at the back of our minds. What is an MSI file? Is it the same as an EXE file? Can it be created and edited by anyone, or is it a sort of system file? What are the prerequisites to extract the contents of an MSI file? Is it possible to run it on an operating system other than Windows, such as Mac or Linux? We, at Buzzle, have answered a number of common queries about MSI-format files hoping they would assist you in understanding everything there is to know about them.
What is an MSI file?
✤ In strictly technical terms, a file with a .MSI format is a database that resembles a structured storage file.

✤ It contains information pertaining to the application program, including details like the procedure of installation, permissions, requirement of user data, and so on.

✤ It generally includes the address at which the compressed version of the program to be installed has been downloaded, although, in some rare cases, the MSI file of a program could contain the file itself.
✤ Nevertheless, a number of different kind of files are stored within the MSI file which can even be accessed individually.

✤ The kind of application programs that can be installed with the help of an MSI file and Windows Installer range from Windows updates to third-party applications.

✤ Unfortunately, a file with this format could act as a virus. Hence, one should always exercise caution before trying to install this file which has been received in an email from an unknown sender.
How does an MSI file differ from an EXE file?
✤ First and foremost, a file that has a .EXE extension does not necessarily have to be an installer, as this extension can be attached to almost any executable file on your computer.

✤ Regarding files that pertain to installation, an EXE file does not contain any data regarding the actual procedure of installation. Instead, it checks whether a compatible version of Windows Installer is available on your computer. If it exists, it acts as the bootstrap for the installation.
✤ Any MSI file itself, compulsorily requires a particular system EXE file to launch it, namely MSIEXEC.EXE

✤ If you do not have a compatible version of Windows Installer in your system, an MSI Redistributable file is launched so as to resolve this anomaly.

✤ Sometimes, the MSI file of an application program as well as an MSI Redistributable file are encapsulated within its EXE file.
How do the various versions of MSI differ?
✤ Various versions of Microsoft Windows Installers have been released by Microsoft over the years. In all, there are five versions currently.

✤ Windows Installer 4.0 was released along with the Microsoft Windows Vista operating system. It stood apart from its predecessors because users could bypass the requirement of entering administrative credentials while installing program packages. This feature could even be provided to users as an option by the developers.
✤ Windows Installer 5.0, which was released along with the Microsoft Windows 7 operating system, took things one step further in favor of the user. It allowed backward compatibility with earlier Windows Installer versions and also gave developers more flexibility with settings and permissions. In simple words, if your computer has Windows Installer 5.0 or higher, you can install software that was designed for a different version of Windows Installer.
✤ Developers of application programs for Windows prefer to use the MSI platform provided by Windows as it helps create an installer package for their software and standardizes it as well.
Is it possible to install individual files from the MSI package?
✤ In general, the files inside an MSI-format file are compressed in some way or the other. While a full installation would mean extracting and executing all the files, individual files too can be separately extracted and run from the package.
✤ This process of individual file extraction from an MSI file can be carried out in two ways. Either it can be done by using the command line interface of Windows, or the files can be extracted using a third-party decompressing software such as 7Zip (an open-source, GNU-licensed "unzipping" software that is used to extract files that are compressed).
✤ A word of caution: Individual files in an MSI package tend to have limitations because they collaborate as a group to install the application program. If you install a few individual files from the package, the program may not get installed correctly on your computer, and hence, won't run.
How does one create an MSI file?
✤ Developers of Windows application programs generally prefer to use the MSI format for their package installer to give their software better outreach. This standard can be used uniformly across the different versions of the Windows operating systems as well as those of Windows Installer.
✤ A number of methods can be used to create MSI files. A developer can even create a package installer for his or her product in this format, right from the development environment. For example, Microsoft Visual Studio and WiX Toolset enable developers to create a .MSI-format package installer using the application's source code.
✤ If coding from scratch is not your forté, a third-party MSI creation tool, such as Windows Advanced Installer, can be used. These have a visual UI and are much simpler to use.

✤ For either method and each individual tool, free tutorials are readily available all over the internet. Microsoft itself clearly spells out how to create an MSI file using Visual Studio in its Support pages.
Is it possible to run an MSI file in Mac or Linux?
✤ The popular method used for this purpose is to make use of a Windows emulator. Wine and CrossOver Mac are good examples of such programs. They create an interface of mutual understanding between the two platforms, which allows data designed for Windows to be translated to a Mac- (or Linux)-compatible format.

✤ The other method is to extract files using a third-party unzipping software such as 7Zip or AlphaZip. Relevant files can be extracted and installed.
✤ An MSI file cannot be run on a non-Windows system as it is. However, certain methods can be used to install an application program that has been compressed into an MSI package, on Mac or Linux.

✤ However, this task can only get you so far as to make your Mac or Linux operating system understand the installation procedure. Whether or not the installed files will function correctly on your computer depends entirely on the application program in question.
We hope that our endeavor to simplify the concepts behind MSI-format files was successful. If any confusion regarding how they work still persists, please leave a comment.