Hercules review
A free, open-source choice for running and testing IBM mainframe software on conventional computers.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Hercules is open-source emulator software for IBM System/370, ESA/390 and 64-bit z/Architecture mainframe systems. It is intended for system programmers, educators, hobbyists and developers who need to run or test mainframe software on conventional computers. Hercules executes guest instructions and channel programs while emulating devices such as DASD storage, tape drives and 3270 terminals. It runs on Linux, Windows, Solaris, FreeBSD and Mac OS X, giving users several host operating system options.
The pricing model is straightforward: Hercules is free and open source. There are no paid tiers described for the product. That keeps the software accessible for users exploring mainframe environments, but the guest operating systems are not included and may require separate licensing. Buyers should therefore account for the software they intend to run rather than treating Hercules as a complete guest operating system package.
Its strongest fit comes from the breadth of its mainframe emulation features. Dynamic reconfiguration supports changes to the emulated system, while DASD shadow files provide snapshot-like state management. TCP/IP connectivity is available through virtual CTC and TUN/TAP interfaces. Hercules also includes the Hercules Automatic Operator for rule-based command automation, along with debug output and CCW tracing for diagnosis. Choose it when IBM mainframe architecture, device emulation and diagnostic control are central requirements. Users seeking a general-purpose emulator or an included guest operating system should consider a different type of software.
Hercules pros and cons
- Where it wins
- Emulates System/370, ESA/390 and z/Architecture instruction sets
- Supports DASD, tape, 3270 terminals and integrated console devices
- Includes networking, snapshots, tracing and rule-based automation
- Where it doesn't
- Guest operating systems are not included
- Mainframe-focused scope may not suit general emulation needs
- Guest operating systems may require separate licensing
Hercules fact sheet, pricing and score →
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