Installation-supplied UIMs must have member names of CBDUCxxx, where xxx is a decimal number from 001 to 256. You can use the HCD facility Query supported hardware and installed UIMs or the Supported Hardware report to find an unused number for a new UIM.

HCD loads UIMs CBDUC001-CBDUC256 and UIMs CBDUS001-CBDUS256 during its initialization.

When option VM_UIM=YES is active in the HCD profile (which is the default), HCD also loads UIMs CBDUC257-CBDUC512 and CBDUS257-CBDUS512.

When option VM_UIM=NO is active in the HCD profile, the range 257 to 512 is not loaded or used. HCD considers range 001-256 as MVS UIMs and 257-512 as VM UIMs.