Hercules-390 Version 4 Official

A new internal debugger with GDB-like syntax, plus enhanced devlist and display commands, made it far easier for system programmers to troubleshoot guest operating systems (MVS, VM/370, z/OS, Linux on Z).

In the landscape of enterprise computing, the mainframe remains a titan—synonymous with unrivaled reliability, scalability, and transactional throughput. For decades, the IBM Z platform has powered the world’s financial systems, airline reservations, and healthcare records. Yet, for students, hobbyists, and even legacy-reliant organizations, gaining access to this ecosystem has traditionally required prohibitively expensive hardware and licensing agreements. Enter Hercules-390, an open-source software emulator that democratized mainframe computing. Among its many iterations, stands as a landmark release: a mature, robust, and feature-complete bridge between the golden age of System/390 and the modern era of commodity hardware.

ipl 0c0 # IPL from DASD device 00C0

Furthermore, Version 4’s modular channel subsystem architecture emulated a wide array of control units: 3270 terminals, 3420 tape drives, 3490 cartridges, and 3380/3390 DASD. For the first time, a full Sysplex (with multiple emulated LPARs communicating over virtual CTC adapters) could be simulated on a single Linux server. System automation tools like NetView and OPS/MVS could be tested and trained upon without reserving a physical mainframe partition.

Hercules 4.x introduces several advancements over its predecessors, focusing on performance, connectivity, and hardware emulation: DOS/360 on Hercules 390 hercules-390 version 4

The most recent stable version, SDL 4.9.1 , was released in December 2025.

While earlier versions (3.xx "Spinhawk") reached a final stable point years ago, is the active development branch. It is maintained by a dedicated community, with the SDL (SoftDevLabs) version being the current standard for users seeking the latest features and bug fixes. A new internal debugger with GDB-like syntax, plus

Released in the late 2000s and maintained through the early 2010s, Hercules-390 Version 4 represents a high-water mark of open source fidelity to a complex proprietary architecture. Its codebase influenced subsequent emulators in other domains (SIMH for DEC, QEMU for various architectures) and provided a reference implementation for ESA/390 that IBM itself has acknowledged as a valuable compatibility tool.