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z390 review

Free#35 of 37 in Emulator Software

A free, open-source choice for running and developing mainframe assembler and COBOL programs.

5.8/10Editor score
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Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026

z390 is a Java-based, open-source toolkit for developing, testing, and running IBM mainframe assembler and COBOL programs on personal computers. It is aimed at mainframe programming education and application development when direct access to a mainframe is not available. The toolkit supports IBM System/360 subset, System/370, System/390, and z/Architecture instruction sets through z17, with Windows, macOS, and Unix-like host support.

Its strongest feature is the breadth of the mainframe development workflow in one package. z390 includes an IBM HLASM-compatible macro assembler, a linker for relocatable object files and load modules, an emulator runtime, and COBOL program execution. It also covers QSAM and VSAM-compatible file processing, TN3270-compatible data streams, and CICS-compatible transaction processing. Interactive execution tracing and test mode add debugging support, while TCP/IP client and server socket services extend the environment beyond local program execution.

The project also offers practical automation options through command-line scripts alongside a graphical interface. That combination suits learners, developers, and teams working with assembler or COBOL code across multiple desktop operating systems. z390 is free and open source, making it a strong fit when the priority is accessible IBM mainframe emulation and development. Its narrower focus makes it less suitable for buyers seeking a broad emulator platform or documented tools for simulating network conditions and capturing emulator state snapshots.

z390 pros and cons

  • Where it wins
    • Supports IBM System/360 through z/Architecture instruction sets through z17
    • Includes assembler, linker, emulator runtime, and COBOL execution
    • Runs on Windows, macOS, and Unix-like systems with GUI and scripts
  • Where it doesn't
    • Its focus is narrower than general-purpose emulator software
    • COBOL and assembler workflows center on IBM mainframe environments
    • Documentation does not describe network-condition simulation or state snapshots

z390 fact sheet, pricing and score →

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