Emulator

Enhanced Definition

An emulator, in the mainframe context, is a software program that allows a non-mainframe system (typically a PC or server) to mimic the behavior of a mainframe terminal (e.g., an IBM 3270 terminal) or, less commonly, a mainframe processor. Its primary purpose is to enable users to interact with mainframe applications and data from remote or distributed environments as if they were directly connected to a physical mainframe terminal.

Key Characteristics

- Terminal Emulation: Most commonly, emulators provide 3270 terminal emulation, allowing a PC to act as a 3270 display station, which is the standard interface for interacting with z/OS, CICS, TSO, IMS, and other mainframe subsystems.
- Protocol Support: They support mainframe communication protocols like TN3270 (Telnet 3270) for TCP/IP networks, enabling secure and reliable connections over modern network infrastructures.
- User Interface: Emulators typically present a character-based, "green-screen" or "blue-screen" interface, replicating the look and feel of a physical 3270 terminal, often with customizable fonts, colors, and screen sizes.
- Function Key Mapping: They map PC keyboard keys (e.g., F1-F12, Enter, Clear) to their corresponding 3270 terminal function keys, allowing users to navigate mainframe applications effectively.
- File Transfer: Many emulators include built-in file transfer capabilities (e.g., IND$FILE utility) to move data between the mainframe and the client workstation.
- Scripting and Automation: Advanced emulators offer scripting languages or macro capabilities to automate repetitive tasks, perform screen scraping, and facilitate data extraction from mainframe sessions.

Use Cases

- Application Development and Testing: Developers use emulators on their workstations to access TSO/ISPF, CICS, or IMS environments for writing, compiling, debugging, and testing COBOL, PL/I, or Assembler programs.
- System Administration: System programmers and administrators use emulators to log into z/OS consoles, issue operator commands, monitor system performance, and manage system resources.
- End-User Access: Business users access critical mainframe applications (e.g., order entry, customer service, financial systems) from their desktops or laptops using terminal emulators.
- Batch Job Monitoring: Emulators are used to view JES job output, SYSOUT, and job logs, allowing operations staff to monitor the status and progress of batch processing.
- Legacy System Integration: Emulators can be part of integration solutions, allowing modern applications to interact with mainframe screens programmatically (often referred to as screen scraping) for data exchange or process automation.

Related Concepts

Emulators are fundamental for interacting with various mainframe subsystems like TSO/ISPF for interactive command processing and development, CICS for online transaction processing, and IMS for hierarchical database and transaction management. They rely on network protocols such as TN3270 to establish communication over TCP/IP networks, connecting the client workstation to the mainframe's VTAM (Virtual Telecommunications Access Method) or z/OS Communications Server. Without emulators, direct interactive access to the mainframe from distributed systems would be impractical or impossible, making them a crucial bridge between distributed and mainframe environments.

Best Practices:

Secure Connections: Always use secure protocols like TN3270S (Telnet 3270 over SSL/TLS) when connecting to the mainframe, especially over public networks, to protect sensitive data in transit.
Centralized Configuration Management: For large deployments, manage emulator configurations centrally to ensure consistency, enforce security policies, and simplify updates and troubleshooting.
Performance Tuning: Optimize emulator settings (e.g., buffer sizes, refresh rates, compression) for network conditions to ensure a responsive and efficient user experience.
Macro and Scripting Governance: While powerful, use scripting features judiciously; implement proper testing and version control for macros to prevent errors and maintain security.
User Training and Documentation: Provide adequate training for users on emulator functions and mainframe application navigation to maximize productivity and minimize support calls.