Each device in a configuration is represented by a unit control block (UCB). In a dynamic configuration environment, a service obtaining UCB information needs to be able to detect any changes in the configuration that could affect the returned information. The MVS™ I/O configuration token provides this capability. You can scan UCBs with the UCBSCAN macro to obtain information about the devices in the configuration. You can also use the UCBINFO macro to obtain device information from a UCB.
The eligible device table (EDT) contains the definitions for the installation's device groups. The EDTINFO macro allows you to obtain information from the EDT.