Windows’ built-in Deployment Image Servicing and Management (DISM) command, a.k.a. dism.exe, is something of a Swiss Army knife when it comes to working on Windows OS images. Among its many capabilities — such as adding optional Windows features and packages, taking image inventories, performing image cleanups, and more — DISM includes an
/Add-Package option. This option allows users to install Microsoft Catalog updates in .cab or .msu files to a targeted Windows image.
.cab is short for “Windows Cabinet,” a type of compressed file that stores data and instructions for Windows that can update device drivers, system files, and so forth. The .msu file extension is associated with the Microsoft Update Standalone Installer. Normally, this installer uses the Windows Update Agent API to install update packages. Both .cab and .msu files also work with the DISM command against Windows image files, which may be of types .wim, .esd, .ffu, or virtual hard disk files of type .vhd or .vhdx.
Note that .msu updates only work on offline images, while the more common .cab files may be applied to an online image to update a running Windows install.
Why use DISM instead of Windows Update?
Good question! Sometimes, DISM provides a way to install an update when Windows Update (WU) may be having issues. At times, Windows Update may simply refuse to work, or it may hang or crash on a particular update. DISM provides a handy way to install updates when WU itself may be unable to oblige.