When you define an I/O configuration, you provide both physical and logical information about these resources. For example, in defining a device you provide physical information, such as its type and model, and logical information, such as the identifier you will assign to the device. Planning your I/O configuration definition describes the information you need to provide for each resource.
You define an I/O configuration to both the operating system (software) and the channel subsystem (hardware).
With Hardware Configuration Definition (HCD), you perform the hardware and software I/O configuration processes through a single, interactive end-user interface. As you enter data, HCD performs validation checking to help avoid data entry errors before you attempt to use the I/O configuration.
The output of HCD is an I/O definition file (IODF), which contains I/O configuration data. An IODF can define multiple hardware and software configurations to the z/OS® operating system. When you activate an IODF, HCD defines the I/O configuration to the channel subsystem or the operating system, or both.
Through the HCD activate function or the MVS™ ACTIVATE operator command, you can make changes to the current configuration without having to initial program load (IPL) the software or power-on reset (POR) the hardware. Making changes while the system is running is known as dynamic configuration or dynamic reconfiguration.
IPL and activation require that you identify the IODF that contains the definition of your configuration. A data set called an I/O configuration data set (IOCDS) is used at POR. An IOCDS can be created from a configuration definition in an IODF. The IOCDS contains the configuration for a specific processor, while the IODF contains configuration data for multiple processors.