Understanding Windows Image Files and Catalog Files

Windows System Image Manager (Windows SIM) uses Windows image (.wim) files and catalog (.clg) files to display the available components and packages that can be added to an unattended answer file. Windows images and catalog files contain configurable settings that you can modify once the component or package is added to an answer file.

Windows Image Files

A Windows image (.wim) file contains one or more compressed Windows images. Each Windows image in a .wim file contains a list of all of the components, settings, and packages available with that Windows image.

Limitations of Windows Image Files

The following list describes some of the limitations of using .wim files.

  • Windows image files can be opened only by an account with administrator privileges.
  • Windows image files can be opened only by one user at a time.
  • Because Windows image files can contain one or more Windows images, they tend to be large. Some Windows image files can be several gigabytes (GB) in size.
  • The settings in a Windows image can change over time. Windows SIM enables you to create an answer file in which the settings are modified, added, or removed. Windows image files also change when packages are added, configured, or removed. By running Setup and then applying the answer file, the new settings and configurations are applied. If you recapture the installed Windows image by using ImageX, the new settings and configurations are now the defaults. When a Windows image changes, you must create a new catalog file.

Because of these limitations, Windows SIM uses catalogs when creating an answer file.

Catalog Files

A "catalog" file is a binary file that lists the state of all the settings and packages in a Windows image. When a catalog is created, it queries the Windows image for a list of all the settings in that image. Because the contents of a Windows image can change over time, it is important that you recreate the catalog file whenever you update a Windows image.

Because Windows images can be opened only by administrators, you must have administrator privileges on the system to create a catalog file.

The Windows retail DVD includes pre-generated catalog files for each Windows image inside install.wim. These catalog files are in the Sources directory of the retail DVD and can be used to create an answer file for a Windows image in the default install.wim file. However, if you intend to create a catalog for a custom Windows image, you should use Image Manager to recreate the catalog for that custom Windows image.

Contents of a Catalog File

The catalog contains the following information:

  • A list of component settings and current values.
  • Windows features and package states.

Benefits of Catalog Files

Catalog (.clg) files have several advantages over .wim files.

  • Significantly smaller than Windows image (.wim) files, .clg files can be less than 1 MB, while .wim files can be several GB in size. Also, .clg files are easier to copy to removable media or a network share.
  • While .clg files enable multiple users to create answer files for a single .clg file at the same time, a .wim file enables only one person to open and to access the .wim file at any given time.
  • Non-administrators can create answer files for a .clg file. However, .wim files can be opened only by administrators.

See Also


Windows SIM Terminology
Windows SIM Architecture
Windows System Image Manager User Interface
Understanding Distribution Shares and Configuration Sets
Understanding Answer Files
Understanding Settings and Properties