A base layer consists of all the files in the reference CVD, excluding a list of files and registry entries specified in the Base Layer Rules policy. The excluded items are the factory policy combined with user-customized base layer rules.

All the data placed on the reference machine is downloaded as part of a base layer. Keep the following considerations in mind when you use reference machines.

Directories that reside directly under the root (C:\) are by default included in the base layer. Do not leave directories in the root that you do not want in the base layer.

Avoid storing unnecessary data on the reference machine. Unnecessary data can consume excessive disk space on the endpoints.

Verify that the Documents and Settings directory does not contain abandoned user profile directories. If an old user directory exists under the Documents and Settings directory and no user profile is registered for it in the system, the system considers it a regular directory and treats it as part of the base layer.

You can exclude specific areas of the reference machine from the base layer. See Working with Base Layer Rules.