Display

Enhanced Definition

In the mainframe context, "Display" refers to the act of presenting information to a user, operator, or log file, typically via a 3270 terminal, an operator console, or a batch job's `SYSOUT` dataset. It is a fundamental method for programs to communicate status, data, and errors to the external environment. In the mainframe context, "Display" refers to the presentation of information to a user, operator, or system component, typically via a 3270 terminal, an operator console, or as output from a batch job. It encompasses both interactive screen-based interfaces and non-interactive output streams.

Key Characteristics

- Primarily associated with character-based output on IBM 3270 terminals or their emulators, often referred to as "green screens," which operate in block mode.
- Achieved programmatically using language constructs like the COBOL DISPLAY verb, Assembler PUT macros, or CICS SEND commands.
- Can be interactive, allowing users to view and respond to information in real-time (e.g., TSO/ISPF, CICS applications).
- Used for presenting system messages and commands on the z/OS operator console, enabling system administrators to monitor and control the system.
- Output from batch jobs is typically directed to SYSOUT datasets, which can then be viewed using utilities like SDSF or printed.
- Often involves screen formatting technologies such as CICS Basic Mapping Support (BMS) or IMS Message Format Service (MFS) for structured and user-friendly screen layouts.

Use Cases

- Presenting application data, input fields, and navigation options to end-users within CICS online transactions or TSO/ISPF panels.
- Outputting status messages, intermediate results, or error diagnostics from a COBOL batch program to its SYSOUT for post-execution analysis.
- Displaying critical system events, resource utilization, and operator commands on the z/OS system console for real-time monitoring and intervention.
- Providing debugging information during program development and testing, allowing developers to trace variable values and program flow.
- Generating reports or summaries directly to a printer or SYSOUT for archival or review, without requiring interactive user presence.

Related Concepts

The DISPLAY verb in COBOL is the primary mechanism for outputting data to the console or SYSOUT, often implicitly writing to SYSOUT in batch. In JCL, the SYSOUT parameter on a DD statement specifies where batch job DISPLAY output is directed. For interactive applications, DISPLAY is intrinsically linked to 3270 terminals and their screen-oriented nature, often managed by **CICS BMS