z390

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What z390 is

z390 is a 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. It supports QSAM/VSAM-compatible file processing, TN3270-compatible data streams, and a CICS-compatible transaction processor. Commands cover macro expansion, assembly, linking, and execution of 390 load modules. With the TEST option, its ez390 emulator offers interactive commands for breakpoints, tracing, and register or memory inspection. Supported instruction sets include the IBM System/360 subset, System/370, System/390, and z/Architecture through z17. It runs on Windows, macOS, and Unix-like systems, including Linux, and requires Java 8 or later. The toolkit is GPLv2 licensed and free. Setup involves installing a Java runtime and unzipping the distribution. One compatibility distinction is that z390 has its own OS services, so SVC calls do not match mainframes; the documentation recommends using its provided OS-based macros.

Who it suits

z390 suits people learning assembler without mainframe access and developers building mainframe applications with modern tooling. It requires Java 8 or later and supports Windows, macOS, and Unix-like systems.

What it does well

Includes compatible assembler and COBOL compiler tools.
Supports QSAM/VSAM files and TN3270 data streams.
Interactive debugging offers breakpoints, tracing, and inspection.
Supports instruction sets through z/Architecture z17.
Free and GPLv2 licensed.

What to know first

Requires Java 8 or later.
SVC calls are not compatible with mainframes.
Uses its own OS services.

Plans

Plan	Billed and limits	Price
z390	GPLv2 licensed · Java 8+ required	Free

As z390development.github.io lists them, read 8 Oct 2026. The maker's own page has the final word.

Verdict

z390 brings assembler and COBOL development, emulation, and debugging tools to supported PC environments. Its OS-service difference matters for programs that rely on mainframe-compatible SVC calls.

Facts from z390's own pages

Assembler: It provides an IBM HLASM compatible macro assembler and macros compatible with common z/OS and z/VSE environments. · z390development.github.io, 8 Oct 2026
COBOL: It includes an IBM Enterprise COBOL compatible compiler. · z390development.github.io, 8 Oct 2026
Commands: The toolkit includes commands to expand macros, assemble, link, and execute 390 load modules. · z390development.github.io, 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. · z390development.github.io, 8 Oct 2026
File processing: It supports QSAM/VSAM compatible file processing. · z390development.github.io, 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. · z390development.github.io, 8 Oct 2026
Intended users: The site names learning assembler without mainframe access and developing mainframe applications with modern tooling as use cases. · z390development.github.io, 8 Oct 2026
License and runtime: The toolkit is GPLv2 licensed and works with Java 8 or later. · z390development.github.io, 8 Oct 2026
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. · z390development.github.io, 8 Oct 2026
Platforms: Installation instructions provide Windows and MacOS/Unix paths, and the command guide describes Windows and Linux/MacOS script directories. · z390development.github.io, 8 Oct 2026
Purpose: z390 is a mainframe assembler and emulator toolkit for developing, testing, and deploying assembler and COBOL programs on a PC. · z390development.github.io, 8 Oct 2026
Support and documentation: The site provides installation instructions, user guides, command references, and reference material, and says documentation contributions are welcome. · z390development.github.io, 8 Oct 2026
Terminal and transactions: It supports TN3270 compatible data streams and a CICS compatible transaction processor. · z390development.github.io, 8 Oct 2026

Where z390 stands on Freedom251

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