A system having no MTL support, that uses an IODF containing MTL definitions, displays error messages such as CBDA384I during IPL or ACTIVATES. Otherwise, the IPL is successful, the UCBs are built correctly, and the devices are treated as standalone devices. If you have a sysplex, you might not want to enable MTL on all your systems at the same time. This might be because of IPL schedules for the various machines (enablement of the full-function code requires an IPL), or you can install MTL and IPL, but find that the work required to update SMS constructs, ACS routines, etc, on all systems is more than you can handle at one time.

Tape drives can be shared between systems. A device defined as MTL resident on one system can be used as a standalone device on a sharing system. This will happen by default if the IODF on the non-MTL system contains no references to the MTL keyword in the definitions. However, environments often require the sharing of IODFs among systems that may be at varying support levels.

To support the sharing of IODFs that contain MTL definitions on systems without MTL support, coexistence is provided in the form of the full-function Tape UIM. This avoids warning messages otherwise issued during IPL or Activate when the MTL feature is encountered in the IODF on the coexisting system. The result is a tape device recognized and initialized as a standalone, non-ATLDS, drive.