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Hercules
What Hercules is
Hercules is an open-source software emulator for IBM System/370, ESA/390, and 64-bit z/Architecture mainframes. It lets a PC execute programs designed for an IBM mainframe and emulates mainframe input and output devices using PC resources, including DASD files and local tn3270 sessions. Hercules does not supply an operating system, so users need to provide one or run a standalone program. With legally licensed operating systems, it can run z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA, and older related IBM systems.
Its features include dynamic reconfiguration, an integrated console, interpretive execution, debugging tools, snapshots and restore, and z/Architecture support. Guest TCP/IP networking can connect to the host through a TUN/TAP interface and the hercifc program; multiple Hercules instances can share devices through client and server instances. The software is free under the Q Public Licence. Downloads include source archives and Windows 32-bit and 64-bit installer and binary packages. The host operating system list includes Linux, Windows, Solaris, FreeBSD, and Mac OS X. Documented unsupported areas include ESCON, FICON, PR/SM, coupling links, and several z/Architecture facilities. The FAQ says Hercules has never claimed production capability and describes its intended role as a system programmer's toy.
Who it suits
Hercules suits system programmers and others who need to run IBM mainframe programs on a PC and can supply a compatible operating system or standalone program. It is also relevant to users who want a free, open-source emulator and can work within its documented limitations.
What it does well
- Emulates System/370, ESA/390, and 64-bit z/Architecture.
- Supports multiple legally licensed IBM operating systems.
- Includes debugging tools, snapshots, and restore.
- Can connect guest TCP/IP networking to the host.
- Free under the Q Public Licence.
What to know first
- Does not provide an operating system.
- Several facilities, including ESCON and FICON, are unsupported.
- The FAQ says it has never claimed production capability.
- Unrestricted access to hercifc can create a security exposure.
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| Hercules | Q Public Licence · source code and binary downloads | Free |
As hercules-390.eu lists them, read 1 Oct 2026. The maker's own page has the final word.
Getting started
- Visit https://www.hercules-390.eu/.
- Choose a source archive or a Windows installer or binary package.
- Use a host operating system from the supported list.
- Provide a legally licensed compatible IBM operating system or a standalone program.
Verdict
Choose Hercules if you need a free emulator for IBM mainframe architectures and can provide a compatible operating system or standalone program. Look elsewhere for production-capable software or for documented support for features such as ESCON, FICON, or coupling links.
Questions
How much does Hercules cost?
Hercules is free under the Q Public Licence.
Which mainframe architectures does it emulate?
It supports System/370, ESA/390, and 64-bit z/Architecture.
Does Hercules include an operating system?
No. Users must supply an operating system or a standalone program.
Which operating systems can it run?
It can run z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA, and older related IBM operating systems when legally licensed.
Which host platforms are supported?
The host operating system list includes Linux, Windows, Solaris, FreeBSD, and Mac OS X. Downloads include source archives and Windows installer and binary packages.
Is Hercules suitable for production use?
Its FAQ says Hercules has never claimed production capability.
Facts from Hercules's own pages
- 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, 1 Oct 2026
- Download formats
- The site offers source archives plus Windows 32-bit and 64-bit installer and binary packages. · hercules-390.eu, 1 Oct 2026
- Execution
- It lets a PC execute programs designed to run on an IBM mainframe. · hercules-390.eu, 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, 1 Oct 2026
- Key features
- Advanced features include dynamic reconfiguration, an integrated console, interpretive execution and z/Architecture support. · hercules-390.eu, 1 Oct 2026
- License
- Hercules is OSI Certified Open Source Software licensed under the Q Public Licence. · hercules-390.eu, 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, 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, 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, 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, 1 Oct 2026
- Security
- The networking documentation warns that unrestricted access to hercifc can create a potential security exposure. · hercules-390.eu, 1 Oct 2026
- Shared devices
- Shared device support allows multiple Hercules instances to share devices through client and server instances. · hercules-390.eu, 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, 1 Oct 2026
- Unimplemented features
- Documented unsupported features include ESCON, FICON, PR/SM, coupling links and several z/Architecture facilities. · hercules-390.eu, 1 Oct 2026
Where Hercules stands on Freedom251
- Emulator Software#20 of 39