The UCB scan service allows you to scan each UCB in the system or in a specified device class. The device classes are: tape, communication, channel-to-channel adapter, direct access, display, unit record, and character reader. Using UCB scan services you can, for example, find the UCB currently associated with a particular VOLSER or find all tape devices currently defined.
The UCB scan service runs in the caller's key, state, and addressing mode. The caller can be in either task or SRB mode; if in task mode, the caller must be enabled and hold no locks. Unlike the IOSLOOK macro, the UCB scan service does not require the user to be in supervisor state or to provide the device number as input.