The OS Layer serves as the foundation for all layered images. For maximum stability and performance, it is a critical best practice to build the OS Layer from a clean, unmodified Windows installation. Furthermore, any Microsoft applications or components that are serviced through the Windows Update mechanism, such as the .NET Framework, Visual C++ Runtimes, or Internet Explorer, must be installed directly into the OS Layer. This ensures that these tightly integrated components are updated in unison with the operating system, preventing versioning conflicts and potential application compatibility issues that could arise if they were placed in a separate App Layer.

A. To update the OS, you add a new version to the existing OS Layer, not create an entirely new layer, which would break compatibility with all other layers.

B. The OS Layer master virtual machine must be in a workgroup and NOT joined to an Active Directory domain to ensure it remains a generic, portable gold image.

C. The Windows Updates feature must be disabled before finalizing the OS Layer to prevent uncontrolled updates on deployed images, ensuring consistency and stability.

1. Citrix App Layering Product Documentation, "Create the OS layer":

Supports Answer E: In the "Prerequisites" section, it states, "Start with a clean OS image... We recommend that you start from an OS that is installed from an ISO."

Supports Answer D: In the "Install the OS and software on the master image" section, it lists required software to be installed in the OS Layer, including ".NET Framework (if required by your version of Windows)" and "Visual C++ runtime libraries." These are updated via Windows Update.

Refutes Answer B: In the "Prerequisites" section, it explicitly states, "The virtual machine must not be joined to a domain."

2. Citrix App Layering Product Documentation, "Update the OS layer":

Refutes Answer A: The entire document describes the process of updating an OS Layer by adding a new version. The first step is, "Select the OS layer that you want to update... and select Add Version."

3. Citrix Tech Zone, "Reference Architecture: Image Management - App Layering":

Refutes Answer C: Under the "OS Layer" section, best practices emphasize control. "Updates to the OS layer are managed by creating a new version of the layer... This process ensures that all updates are tested and validated before being deployed to production." This implies disabling automatic updates on the final image.