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MSI (Windows Installer) file format

.msi  ·  installer database  ·  introduced 1999 by Microsoft

What is a MSI (Windows Installer) file?

MSI files are Microsoft Windows Installer packages. They are not pure archives but small relational databases (in OLE Compound File format) describing files, registry edits, and install actions, often with embedded or external CAB archives. Enterprise admins love MSI because it can be deployed silently via Group Policy and uninstalled cleanly.

Most readers reach this page after double-clicking a .msi file and finding their operating system unsure what to do with it. The good news: MSI (Windows Installer) is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.

How to extract a MSI (Windows Installer) file

Opening a .msi file is straightforward on every modern operating system. The exact steps depend on which platform you are on:

On Windows

  1. Locate the .msi file in File Explorer.
  2. Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
  3. If prompted, pick a destination folder and click Extract.
  4. The extracted files appear in a folder next to the original archive.

On macOS

  1. Find the .msi file in Finder.
  2. Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
  3. Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
  4. The extracted folder appears next to the archive.

On Linux

  1. Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
  2. On the command line, run one of: 
    7z x archive.msi    # works for almost any format
  3. The files appear in the current directory.

How to create a MSI (Windows Installer) file

To pack files into a .msi archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write MSI (Windows Installer).

On the command line, the canonical create command is:

# Use 7-Zip, PeaZip, or the format's reference tool to create .msi files.

If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.

Strengths

  • Standard Windows install plumbing
  • Silent install / uninstall
  • Repair mode

Weaknesses and limitations

  • Windows-only
  • Authoring tools are heavy (WiX, InstallShield)

Typical use cases

  • Enterprise Windows software deployment
  • Group Policy software install
  • Silent installs (msiexec /qn)

Technical details

MSI (Windows Installer) uses the Compound File Binary + CAB payload algorithm and is identified on disk by the magic byte sequence D0 CF 11 E0 A1 B1 1A E1. The standard MIME type is application/x-msi. The format is a proprietary specification and is free for any use.

Frequently asked questions

Is MSI (Windows Installer) safe to open?

Archive files are containers — they are only as safe as what they contain. A .msi from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.

What is the maximum file size?

Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).

Can I password-protect a MSI (Windows Installer)?

Some archivers can wrap MSI (Windows Installer) files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.

How does MSI (Windows Installer) compare to other formats?

See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.

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