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Windows Updates: CAB vs MSU Files

This morning, TenForums reported that Microsoft released a new Cumulative Update KB3197356 for Windows 10. But though some users have reported obtaining this through Windows Update, users who’ve successfully installed the previous update — KB3194496 — probably won’t get this latest roll-up. Those who want it anyway must visit the Microsoft Update Catalog so they can download and install it manually themselves. While this particular update is a Windows Standalone Installer (MSU) file, other updates can appear as Cabinet (CAB) files, particularly device drivers. That got me wondering about differences between the two formats. So, I researched CAB vs MSU files and report on what I learned.

The update elements for KB3197356 are .MSU files, other downloads are .CAB files. What gives?
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Understanding CAB vs MSU Files

MSU files are associated with the Windows Standalone Update Installer, of type Microsoft Update Standalone Package. Thus, this program is called when any filename ending in .msu is executed. Device drivers, on the other hand, don’t always need a special installer. Instead, you might access their contents using the “Update Driver Software…” right-click option in Device Manager. Also, CAB files are archives that support a variety of compression formats. They work with various Windows installation engines. These include the Setup API, device installers, or advpack.dll.  Whatis.com says: “CAB files typically contain drivers, system files and other Windows components.”

Here’s the core of the difference, in a nutshell. MSU files are more or less self-installing, thanks to the Standalone Update Installer program included with Windows OSes. But double-clicking a CAB file gets you nowhere automatically. You must either invoke the right installation engine, or otherwise access its contents. Much of the time, a program like 7zip does the trick nicely. But those who remain perplexed will find the Windows 10 CAB Installer (download links: x86/32-bit, x64/64-bit) helpful in using CAB contents (source: TenForums).

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