IODF
The I/O definition file: the dataset that describes all the hardware connected to the mainframe, such as disks, tape drives and network devices.
Also written I/O definition file, HCD, Hardware Configuration Definition, I/O configuration, device number
Every disk volume, tape drive and network adapter that z/OS uses must be defined before it can be used. The definitions are kept in the IODF, the I/O definition file. It records the channels that connect the machine to its devices, the control units the devices sit behind, the devices themselves with their device numbers, and which LPARs may use them.
The IODF is created and changed with HCD, the Hardware Configuration Definition tool, which checks that the definitions make sense together. Both the machine and z/OS read the IODF: the machine to set up its connections, and z/OS to know which devices exist.
Many changes can be made without an IPL. A new IODF can be activated on a running system, which adds new devices or removes old ones.
Device numbers from the IODF appear in many places, such as the device address given for an IPL and in messages about a disk or tape drive. Hardware configuration is specialist work, usually done by a small team, but the device numbers it creates are used by everyone.
Where can I learn this hands-on?
Right here, at ZedBank. You take a junior job at a simulated bank and learn each part of the work by doing it, with Zed beside you. There's nothing to install.
Start at ZedBankRelated
- IPLInitial program load: starting z/OS on a system, the mainframe word for booting.
- LPARA logical partition: one physical mainframe carved into several independent virtual machines, each running its own operating system.
- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- System programmerThe person who installs, configures, tunes and upgrades the operating system and its subsystems.
- HMCThe Hardware Management Console: the workstation used to control the mainframe hardware, its LPARs and IPLs.
- DASDDirect access storage device, the mainframe term for disk storage.