Scenario: A Citrix Administrator wants to add machines to a Delivery Group. The administrator has two machine catalogs containing unallocated…

A fundamental rule when managing Delivery Groups in Citrix Virtual Apps and Desktops is that all machines within a single Delivery Group must be of the same OS type. The type is determined by the first machine catalog added to the group. For example, if a Delivery Group is created with a multi-session OS catalog (e.g., Windows Server), you cannot later add machines from a single-session OS catalog (e.g., Windows 10). The user interface will filter out and hide any machine catalogs that do not match the OS type of the existing Delivery Group, which explains why the second catalog is not visible.

B. provisioned with another provisioning method: A single Delivery Group can contain machines from multiple catalogs that use different provisioning methods (e.g., one using MCS and another using PVS), as long as they share the same OS type.
C. unregistered: The registration state of a machine does not prevent its catalog from being added to a Delivery Group. An administrator can add unregistered machines; they will simply appear as "Unregistered" within the group.
D. turned off: A machine's power state (on or off) is irrelevant when adding it to a Delivery Group. Power management settings within the Delivery Group control when machines are powered on.

1. Citrix Virtual Apps and Desktops Product Documentation, "Create Delivery Groups": In the "Step 2. Machines" section, the documentation states, "All machines in a Delivery Group must be of the same machine type (multi-session OS or single-session OS). That machine type is established the first time you add a catalog to the group." This directly confirms that a mismatch in OS type will prevent a catalog from being available.

2. Citrix Virtual Apps and Desktops Product Documentation, "Manage Delivery Groups": The section on "Add machines" reinforces this principle. When adding machines to an existing group, the wizard only displays catalogs containing machines of the same type (single-session or multi-session OS) as those already in the group.