z390
z390 is a free, GPLv2-licensed mainframe assembler and emulator toolkit for developing, testing, and deploying assembler and COBOL programs on a PC.
What z390 is
z390 is a free, GPLv2-licensed mainframe assembler and emulator toolkit for developing, testing, and deploying assembler and COBOL programs on a PC. It includes an IBM HLASM-compatible macro assembler, macros for common z/OS and z/VSE environments, and an IBM Enterprise COBOL-compatible compiler. File processing supports QSAM/VSAM-compatible operations, while terminal and transaction features cover TN3270-compatible data streams and a CICS-compatible transaction processor. Commands expand macros, assemble, link, and execute 390 load modules. With the TEST option, the ez390 emulator provides breakpoints, tracing, and register or memory inspection. Supported targets include the IBM System/360 subset, System/370, System/390, and z/Architecture instruction sets through z17. Hosts include Windows, macOS, and Unix-like systems, with Java 8 or later required. Installation involves unzipping the distribution after installing Java. z390 suits assembler learners without mainframe access and developers using modern tooling. Its OS services differ from mainframes, so SVC calls are not compatible.
Good
- Includes HLASM-compatible macro assembly
- Provides an Enterprise COBOL-compatible compiler
- Supports QSAM/VSAM file processing
- Offers emulator breakpoints and tracing
- GPLv2 licensed and free
Watch out
- Requires Java 8 or later
- SVC calls are not mainframe-compatible
- Installation requires manual unzipping
- Targets are limited to listed IBM instruction sets
Who it suits
It suits learners practicing assembler without mainframe access and developers building or testing mainframe applications on a PC. Users should be comfortable with Java installation and the toolkit’s distinct OS services.
Verdict
z390 combines assembly, COBOL, emulation, file processing, transaction support, and debugging for several IBM instruction-set families. Its free license and broad host support are balanced by Java requirements and non-mainframe SVC behavior.
Plans and prices
From z390's own pricing page, checked 8 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| z390 | Free | GPLv2 licensed · Java 8+ required |
The facts
Each one read from z390's own pages, with the date it was checked.
What it does
- Assembler
- It provides an IBM HLASM compatible macro assembler and macros compatible with common z/OS and z/VSE environments.checked 8 Oct 2026
- COBOL
- It includes an IBM Enterprise COBOL compatible compiler.checked 8 Oct 2026
- Commands
- The toolkit includes commands to expand macros, assemble, link, and execute 390 load modules.checked 8 Oct 2026
- Debugging
- The ez390 emulator supports interactive test commands when the TEST option is specified, including breakpoints, tracing, and register or memory inspection.checked 8 Oct 2026
- File processing
- It supports QSAM/VSAM compatible file processing.checked 8 Oct 2026
- Installation
- Installation consists of unzipping the distribution to the local file system after installing a Java runtime environment version 8 or above.checked 8 Oct 2026
- Intended users
- The site names learning assembler without mainframe access and developing mainframe applications with modern tooling as use cases.checked 8 Oct 2026
- License and runtime
- The toolkit is GPLv2 licensed and works with Java 8 or later.checked 8 Oct 2026
- Purpose
- z390 is a mainframe assembler and emulator toolkit for developing, testing, and deploying assembler and COBOL programs on a PC.checked 8 Oct 2026
- Support and documentation
- The site provides installation instructions, user guides, command references, and reference material, and says documentation contributions are welcome.checked 8 Oct 2026
- Terminal and transactions
- It supports TN3270 compatible data streams and a CICS compatible transaction processor.checked 8 Oct 2026
Where it runs
- OS compatibility limit
- SVC calls are not compatible with mainframes because z390 implements its own different OS services; the documentation recommends using its provided OS based macros.checked 8 Oct 2026
- Platforms
- Installation instructions provide Windows and MacOS/Unix paths, and the command guide describes Windows and Linux/MacOS script directories.checked 8 Oct 2026
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