Use the LOCANY parameter on the Hardware Configuration Definition (HCD) panel to define unit control blocks (UCBs) either above or below the 16 MB line. Each device attached to the system has one or more UCBs associated with it. To conserve common virtual storage below the 16 MB line, you can define a UCB for a device above 16 MB.
Related reading: For more information, see z/OS HCD User's Guide.