Full Screen

Enhanced Definition

In the context of IBM mainframe systems, "Full Screen" refers to an interactive display mode where an entire screen of a 3270-type terminal (or its emulator) is presented to the user, allowing for character-based input and output. Unlike line-mode interfaces, full -screen applications manage the entire display area, enabling structured data entry and presentation through defined fields.

Key Characteristics

- 3270 Terminal Emulation: Relies on the architecture of IBM 3270 Information Display Systems, which are block-mode, character-oriented terminals, not graphical.
- Character-Based Interface: All display elements, including text, fields, and basic graphics (like lines or boxes), are rendered using characters from the EBCDIC character set.
- Screen Buffer: The terminal maintains a screen buffer that holds the entire display content. Application programs manipulate this buffer, and changes are sent to the terminal in blocks, not character-by-character.
- Field Attributes: Data entry and display areas are defined as fields, each with attributes like protected/unprotected, numeric-only, display-only, intensity (normal, high), color, and highlighting, controlled by the application.
- Programmatic Control: Application programs (e.g., COBOL, PL/I, Assembler) use specific APIs or screen mapping facilities (like BMS for CICS, MFS for IMS, or ISPF Dialog Manager) to define screen layouts and interact with users.
- Block Mode I/O: User input is typically buffered until an attention key (e.g., Enter, PF key, PA key) is pressed, at which point the entire modified screen content (or just the modified fields) is transmitted to the host.

Use Cases

- TSO/ISPF Panels: The primary interface for mainframe developers and system programmers, providing full-screen editors (ISPF Edit), file managers, job submission, and system utilities.
- CICS Transactions: Online transaction processing applications (e.g., banking, airline reservations) use full-screen maps to guide users through data entry and display results quickly and efficiently.
- IMS DC Applications: Similar to CICS, IMS Database/Data Communications applications utilize Message Format Services (MFS) to define and manage full-screen interactions with terminal users for data entry and query.
- System Monitoring and Control: Tools like SDSF (System Display and Search Facility), NetView, and OMEGAMON provide full-screen interfaces for monitoring system performance, managing jobs, and controlling network resources.
- Custom User Applications: Many legacy and modern custom-built applications on z/OS continue to use full-screen interfaces for interactive data entry, query, and reporting due to their efficiency and familiarity.

Related Concepts

Full -screen interaction is fundamentally tied to the 3270 Data Stream protocol, which defines how data and control information are exchanged between the host and the terminal. It relies on VTAM (Virtual Telecommunications Access Method) for network communication, allowing terminals to connect to various host applications. Application programs written in languages like COBOL, PL/I, or Assembler leverage specific screen mapping facilities (e.g., CICS BMS, IMS MFS, ISPF Dialog Manager)