VTOC
The volume table of contents: the list on each disk volume of which datasets it holds and exactly where they are.
Also written volume table of contents, DSCB, VTOC index
VTOC stands for volume table of contents. Every disk volume has one. It lists each dataset on that volume, where on the volume its space is, and its attributes, such as record format, record length and block size. It also keeps track of the free space that is left.
The VTOC and the catalog work together. The catalog answers "which volume is this dataset on?" The VTOC on that volume answers "where on this volume is it, and what is it like?" Finding a dataset by name is a two-step lookup: catalog first, then VTOC.
Because the VTOC belongs to the volume, it knows about every dataset on it, even one that was never catalogued. That is how a dataset can exist on a disk but not be found by name.
The VTOC has a fixed size. If it fills up, no new datasets can be created on that volume even when there is free space left. You will rarely look at a VTOC directly, but messages about VTOC space, or a dataset "found on the volume but not in the catalog", will make sense once you know it is there.
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
- VolumeA single unit of disk storage with a six-character label, on which datasets are placed.
- DASDDirect access storage device, the mainframe term for disk storage.
- CatalogThe system's index of where datasets live, so you can refer to a dataset by name without knowing which disk it is on.
- DatasetWhat a mainframe calls a file: a named collection of records with a defined structure, rather than a loose stream of bytes.
- Space allocationReserving disk space for a dataset up front, in tracks, cylinders or blocks, with room to grow.