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Hercules
What it is
Hercules is free, open-source software that emulates IBM System/370, ESA/390, and 64-bit z/Architecture mainframes. It lets a PC run programs designed for those architectures and represents mainframe input and output devices with PC resources, including DASD files and local tn3270 sessions. Hercules does not include an operating system, so users must provide a legally licensed compatible IBM system or a standalone program. Supported systems include z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA, and older related systems. Features include dynamic reconfiguration, an integrated console, interpretive execution, debugging tools, snapshots and restore, network simulation, and z/Architecture support. Guest TCP/IP networking can connect through a TUN/TAP interface and hercifc, while separate Hercules instances can share devices through client and server connections. The software runs on Linux, macOS, and Windows, with host support also listed for Solaris and FreeBSD. It is licensed under the Q Public Licence. Documented unsupported areas include ESCON, FICON, PR/SM, coupling links, and several z/Architecture facilities. The FAQ describes it as a system programmer's toy rather than production-capable software.
For and against
For
- Free Q Public Licence software
- Supports System/370, ESA/390, and z/Architecture
- Runs programs built for IBM mainframes
- Networking through TUN/TAP and hercifc
- Snapshots, restore, and debugging tools
Against
- Does not provide an operating system
- Some mainframe features remain unsupported
- FAQ says it is not production-capable
- Networking access can create security exposure
The verdict
Hercules provides a broad emulator for experimenting with and running compatible IBM mainframe software on supported PCs. Users must supply an operating system, account for unsupported facilities, and treat its non-production positioning seriously.
Who it suits
Hercules suits system programmers, learners, and others who need to run legally licensed IBM mainframe software on a PC. It is not positioned as production-capable software.
Plans and prices
Hercules
Q Public Licence · source code and binary downloads
Read 1 Oct 2026 · hercules-390.eu
On the record
- Architecture support
- The emulator can run z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA and older related IBM operating systems when legally licensed.hercules-390.eu · read 1 Oct 2026
- Download formats
- The site offers source archives plus Windows 32-bit and 64-bit installer and binary packages.hercules-390.eu · read 1 Oct 2026
- Execution
- It lets a PC execute programs designed to run on an IBM mainframe.hercules-390.eu · read 1 Oct 2026
- I/O emulation
- Hercules emulates mainframe I/O devices using PC devices, including DASD files and local tn3270 sessions.hercules-390.eu · read 1 Oct 2026
- Key features
- Advanced features include dynamic reconfiguration, an integrated console, interpretive execution and z/Architecture support.hercules-390.eu · read 1 Oct 2026
- License
- Hercules is OSI Certified Open Source Software licensed under the Q Public Licence.hercules-390.eu · read 1 Oct 2026
- Networking
- Hercules can connect guest TCP/IP networking to the host through a TUN/TAP interface and its hercifc program.hercules-390.eu · read 1 Oct 2026
- Operating systems
- Hercules does not provide operating-system facilities, so users must supply an operating system or standalone program.hercules-390.eu · read 1 Oct 2026
- Production suitability
- The FAQ says Hercules has never claimed to be production-capable and was intended as a system programmer's toy.hercules-390.eu · read 1 Oct 2026
- Purpose
- Hercules is an open-source software implementation of the System/370, ESA/390 and 64-bit z/Architecture mainframe architectures.hercules-390.eu · read 1 Oct 2026
- Security
- The networking documentation warns that unrestricted access to hercifc can create a potential security exposure.hercules-390.eu · read 1 Oct 2026
- Shared devices
- Shared device support allows multiple Hercules instances to share devices through client and server instances.hercules-390.eu · read 1 Oct 2026
- Support
- Paid technical support may be available through Open Source Mainframes, Inc., while free support is provided through Hercules discussion forums.hercules-390.eu · read 1 Oct 2026
- Unimplemented features
- Documented unsupported features include ESCON, FICON, PR/SM, coupling links and several z/Architecture facilities.hercules-390.eu · read 1 Oct 2026
