What Is an MSI File?

How to open, edit, and convert MSI files

A file with the .MSI file extension is a Windows Installer Package file. It's used by some versions of Windows when installing updates from Windows Update, as well as by third-party installer tools.

An MSI file holds all the information necessary for installing the software, including the files that should be installed and where on the computer those files should be installed to.

"MSI" originally stood for the title of the program that works with this format, which was Microsoft Installer. However, the name has since changed to Windows Installer, so the file format is now the Windows Installer Package file format.

MSI files in a folder.
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MSU files are similar but are Windows Vista Update Package files used by Windows Update on some versions of Windows, and installed by the Windows Update Standalone Installer (Wusa.exe).

How to Open MSI Files

Windows Installer is what the Windows operating system uses to open MSI files when they're double-clicked. This doesn't need to be installed to your computer or downloaded from anywhere because it's built-in to Windows. Just opening the MSI file should invoke Windows Installer so you can install the files that are contained within it.

MSI files are packed in an archive-like format, so you can actually extract the contents with a file unzip utility like 7-Zip. If you have that or a similar program installed (most of them work similarly), you can right-click the MSI file and choose to open or extract the file to see all the files that are stored inside.

Using a file unzip tool is also useful if you want to browse the MSI files on a Mac. Since the MSI format is used by Windows, you can't just double-click it on a Mac and expect it to open.

Keep in mind that being able to extract the parts that make up an MSI file does not mean that you can "manually" install the software the MSI would do for you automatically.

How to Convert an MSI File

To convert MSI to ISO is possible only after you extract the files to a folder. Use a file unzip tool like we described above so that the files can exist in a regular folder structure. Then, with a program like WinCDEmu installed, right-click the folder and select Build an ISO image.

Another option is to convert MSI to EXE, which you can do with Ultimate MSI to EXE Converter. The program is very simple to use: select the MSI file and choose where to save the EXE file. There aren't any other options.

Introduced in Windows 8 and similar to MSI, APPX files are app packages that run on the Windows OS. Visit Microsoft's website if you need help converting MSI to APPX. Also, see the tutorial at CodeProject.

How to Edit MSI Files

Editing MSI files isn't as straightforward and easy as editing most other file formats like DOCX and XLSX files because it's not a text format. However, Microsoft does have the Orca program, as part of the Windows Installer SDK, that can be used to edit an MSI file.

You can also use Orca in a standalone format without needing the whole SDK. Technipages has a copy here. After you install Orca, just right-click an MSI file and choose Edit with Orca.

Still Can't Open Your File?

Given the number of file formats out there, and that most of them use a file extension that's just three letters long, it would make sense that many would use some of the same letters. This can get pretty confusing when they're spelled almost identically.

However, it's important to realize that two similarly spelled file extensions doesn't necessarily mean that the file formats are similar or that they can open with the same software. You could have a file that looks an awful lot like the extension says "MSI" but it really doesn't.

For example, MIS files are either Marble Blast Gold Mission or Saved Game Mission files used by some video games, and they have absolutely nothing to do with Windows Installer.

Another is the MSL file extension that belongs to Mapping Specification Language files and Magick Scripting Language files. The former file type works with Visual Studio and the latter with ImageMagick, but neither work anything like MSI files.

The bottom line: if your "MSI" file won't open, make sure you're actually dealing with an MSI file by double-checking the file extension.