The HCD unit information modules (UIMs) are a set of modules, apart from HCD, that describe the characteristics of a device, control unit, and ESCON director, supported by z/OS MVS or VM. (From now on, this book will use the term I/O unit for all types of I/O equipment, such as device, control unit, and ESCON director.) UIMs are involved in the validation of user input to HCD. They are also used at IPL or dynamic activation time to build the unit control blocks (UCBs). Only I/O units that are supported by UIMs can be configured with HCD and included in the IPL process.

IBM supplies a set of UIMs listed in IBM-Supplied UIMs. IBM-supplied UIMs are provided with HCD and with the device support code that you have installed. The UIMs provided with the device support code define the device values for z/OS MVS systems. The UIMs provided with HCD complement the device values for VM systems. Use the HCD Query supported hardware and installed UIMs function to display a list of:

• Supported I/O devices
• Supported control units
• Supported switches (ESCON directors)
• UIMs

In addition, you can use the HCD batch utility "Print a Configuration or Supported Hardware Report" to print the actual status of hardware supported in your installation:

• Processors
• Control units
• Devices