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SPECIFICTION
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Hercules

hercules-390.eu

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Spec score 7.8 #25 of 39 in Emulator Software

What it is

Hercules is a free, open-source emulator for IBM System/370, ESA/390, and 64-bit z/Architecture mainframes. It lets a PC execute programs designed for those systems and represents mainframe I/O devices with PC resources, including DASD files and local tn3270 sessions. It does not provide an operating system, so users must supply one or run a standalone program. With legally licensed software, it can run z/OS, z/VM, z/VSE, OS/390, VM/ESA, VSE/ESA, and older related IBM operating systems. Features include dynamic reconfiguration, an integrated console, interpretive execution, debugging tools, and snapshots and restore. Guest TCP/IP networking can connect to the host through TUN/TAP and hercifc, and multiple instances can share devices. Hercules is licensed under the Q Public Licence and runs on Linux, macOS, and Windows; the host list also names Solaris and FreeBSD. Documented unsupported areas include ESCON, FICON, PR/SM, coupling links, and several z/Architecture facilities. Its FAQ says it has not claimed production capability and was intended as a system programmer's toy.

Spec sheet

Purpose
Hercules is an open-source software implementation of the System/370, ESA/390 and 64-bit z/Architecture mainframe architectures.Read 1 Oct 2026 · hercules-390.eu
Security
The networking documentation warns that unrestricted access to hercifc can create a potential security exposure.Read 1 Oct 2026 · hercules-390.eu
Support
Paid technical support may be available through Open Source Mainframes, Inc., while free support is provided through Hercules discussion forums.Read 1 Oct 2026 · hercules-390.eu
License
Hercules is OSI Certified Open Source Software licensed under the Q Public Licence.Read 1 Oct 2026 · hercules-390.eu
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.Read 1 Oct 2026 · hercules-390.eu
Download formats
The site offers source archives plus Windows 32-bit and 64-bit installer and binary packages.Read 1 Oct 2026 · hercules-390.eu
Execution
It lets a PC execute programs designed to run on an IBM mainframe.Read 1 Oct 2026 · hercules-390.eu
I/O emulation
Hercules emulates mainframe I/O devices using PC devices, including DASD files and local tn3270 sessions.Read 1 Oct 2026 · hercules-390.eu
Key features
Advanced features include dynamic reconfiguration, an integrated console, interpretive execution and z/Architecture support.Read 1 Oct 2026 · hercules-390.eu
Networking
Hercules can connect guest TCP/IP networking to the host through a TUN/TAP interface and its hercifc program.Read 1 Oct 2026 · hercules-390.eu
Operating systems
Hercules does not provide operating-system facilities, so users must supply an operating system or standalone program.Read 1 Oct 2026 · hercules-390.eu
Production suitability
The FAQ says Hercules has never claimed to be production-capable and was intended as a system programmer's toy.Read 1 Oct 2026 · hercules-390.eu
Shared devices
Shared device support allows multiple Hercules instances to share devices through client and server instances.Read 1 Oct 2026 · hercules-390.eu
Unimplemented features
Documented unsupported features include ESCON, FICON, PR/SM, coupling links and several z/Architecture facilities.Read 1 Oct 2026 · hercules-390.eu

Plans and prices

Hercules Free Q Public Licence · source code and binary downloads Read 1 Oct 2026 · hercules-390.eu

Every Hercules plan and price →

Strong points and limits

Strong points

  • Free under the Q Public Licence.
  • Supports System/370, ESA/390, and z/Architecture targets.
  • Includes debugging tools, snapshots, and restore.
  • Can connect guest TCP/IP networking to the host.

Limits

  • Does not include an operating system.
  • Several features, including ESCON and FICON, are unsupported.
  • The FAQ does not claim production capability.
  • Unrestricted hercifc access can create a security exposure.

Who it suits

Hercules suits system programmers who want to run mainframe software on a PC and can provide a compatible, legally licensed operating system or standalone program. Its stated role and documented unsupported features make workload fit important to consider.

Verdict

Hercules offers a free way to execute mainframe programs on a PC, with networking, debugging, and device-sharing capabilities. It requires users to supply an operating system or standalone program, and its own FAQ does not claim production capability.

Where Specifiction places it

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