If your configuration contains an I/O unit that is not supported by any supplied UIM and that cannot be substituted by an IBM device type, you can use the NOCHECK or DUMMY control unit and the DUMMY device. These control units and devices do not provide the full amount of HCD validation.

NOCHECK control unit

A control unit defined as NOCHECK allows any specifications; for example, any protocol can be specified or any device can be connected to it.

DUMMY control unit

A control unit defined as DUMMY can connect only DUMMY devices.

DUMMY device

A device defined as DUMMY is treated as a unit record device.

If your configuration contains an I/O unit that is not supported by any supplied UIM, and the NOCHECK or DUMMY control units or the DUMMY device cannot be used because certain validations should be performed at definition time, you need to provide an installation-written UIM. The following chapters explain how to write your own UIM.