gtpc3m17 | Concepts and Structures |
Unit record equipment can also be used by low priority online batch-oriented Entries (such as report generators) that require printers or card readers as input/output (I/O) devices. If indiscriminately activated, Entries utilizing unit record equipment can impact the performance of the TPF system. Priority job tables in the Unit Record Message Editor program permit low priority unit record Entries to be activated only when a predefined number of main storage blocks are available. Higher priority Entries can be activated any time; therefore operator discretion is needed. An abort procedure is provided but requires a rerun of the Entry because no restart mechanism is provided.
Like general tapes, unit record devices are assigned to Entries. This ensures consecutive printing and card reading. However, unlike general tapes, no reserve unit record function is provided to pass control of unit record devices to another Entry for further processing.
Unit record device addresses are assigned to a particular CPC.