What is a .msi file?
Windows Installer Package · Disk image · Microsoft · 1999
An MSI is a Windows Installer package: a database of files and rules that Windows uses to install, repair and cleanly uninstall a program. You do not really open an MSI, you run it, and Windows does the installation.
What is a .msi file used for?
MSI is the format behind Add or Remove Programs. Instead of a one-off setup program, it is a structured database that tells the Windows Installer service exactly what to copy, register and undo, which is why MSI apps uninstall and repair cleanly.
Under the hood an MSI is an OLE2 compound file, the same container legacy Office documents use, so its first bytes match .doc and .xls. The extension, not the signature, is what tells the two apart.
Double-clicking an MSI installs it. IT admins install silently from the command line with msiexec (for example msiexec /i app.msi /quiet) and deploy MSIs across a network with Group Policy.
To look inside without installing, a tool like 7-Zip can list the packaged files. MSI is Windows-only; other systems cannot install one natively.
What opens a .msi file?
The .msi format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.
Windows
- Double-click to install
- msiexec (command line install)
- 7-Zip (to inspect contents)
macOS
- Not natively supported
- 7-Zip / msitools (to inspect only)
Linux
- Not natively supported
- msitools (to inspect)
- Wine (limited)
Web
- Not applicable
Open a .msi file step by step
- Confirm the file really is a .msi. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
- On Windows, open it with Double-click to install or msiexec (command line install).
- On Mac, use Not natively supported or 7-Zip / msitools (to inspect only).
- On Linux, try Not natively supported or msitools (to inspect).
- Still stuck? Convert the .msi to Not convertible, which opens more widely.
Why can't I open my .msi file?
Almost always because no installed app understands MSI. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.
The other possibility is that the file is not really a .msi at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.
How to convert a .msi file
You can convert a .msi file to Not convertible using a conversion tool or the export menu of an app that opens it.
What is the .msi file signature (magic bytes)?
A .msi file starts with the hex bytes D0 CF 11 E0 A1 B1 1A E1. Programs identify MSI by those bytes, not by the filename, so a renamed file still gives itself away.
These are the documented signatures for MSI. For a full breakdown, see the OLE2 Compound File file signature page.
| Hex signature | Offset | ASCII | Note |
|---|---|---|---|
| D0 CF 11 E0 A1 B1 1A E1 | 0 | - | OLE2 compound file, shared with legacy Office .doc/.xls/.ppt |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .msi file?
An MSI is a Windows Installer package: a database of files and rules that Windows uses to install, repair and cleanly uninstall a program. You do not really open an MSI, you run it, and Windows does the installation.
How do I open or install an MSI file?
Double-click it and follow the installer, or from a command prompt run msiexec /i path\to\file.msi. To inspect the contents without installing, open the MSI in 7-Zip.
What is the difference between an MSI and an EXE installer?
An EXE installer is a program that runs setup however its author coded it. An MSI is a standard database the Windows Installer service processes, which gives Windows consistent install, repair and uninstall, plus silent and network deployment. Many EXE installers simply wrap an MSI inside.
Is an MSI file safe?
Only if you trust the source. Installing an MSI lets it add or change software on your computer, so download packages from the official vendor and be cautious with any MSI you did not expect.
Related formats
Sources
Details on this page were checked against authoritative references. How sources are ranked and what is deliberately left out is set out in the methodology.