How z/OS and Other Vendor Products Eliminate Eligibility of Devices

Devices can be eliminated from eligibility for allocation for a variety of reasons. Some common examples are:

z/OS eliminates devices that are offline, inaccessible, or allocated.
TPCF eliminates devices reserved for other jobs, devices marked OVERGENNED according to the SETOPTION TPCF OVGINELIG parameter, and devices specified by the TPCEDLXT exit.
Robotic software eliminates devices based on the existence of the device inside or outside the robot.

Any preferencing applied to devices eliminated from allocation is ineffective because these devices cannot be chosen for allocation.