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The Hercules System/370, ESA/390, and z/Architecture Emulator

Hercules is an open source software implementation of the mainframe System/370 and ESA/390 architectures, in addition to the new 64-bit z/Architecture. Hercules runs under Linux, Windows 98, Windows NT, and Windows 2000.

Hercules was created by Roger Bowler and is maintained by Jay Maynard. Jan Jaeger designed and implemented many of the advanced features of Hercules, including dynamic reconfiguration, integrated console, interpretive execution and z/Architecture support.

Follow these links to find out more:

Download the current release version, 2.16.5:

The complete source code for the current development version of Hercules is also available via anonymous access from our cvs source code repository. The cvs root is Doing a checkout on module "hercules" will get you the source for all of Hercules, and checking out "wingui" will get you the complete source for the Windows GUI front end (HercGUI).

No password is required; just press enter when asked:

cvs login
(Logging in to
CVS password:
cvs -z9 co hercules
cvs server: Updating hercules

Please note that this will get you the current development version of Hercules, which is not release quality and thus might not even work (since it's still under development). If you want the current, stable, release version of Hercules (i.e. one that is known to work properly), then use the previously mentioned links instead.

Read the file README.CVS for additional and updated instructions for building the development version.

What people are saying about Hercules

“ Never in my wildest dreams did I expect to see OS running on a machine that I personally own. Hercules is a marvelous tool. My thanks to you all for a job very well done. ”
— Reed H. Petty

“ I do miss my mainframe a lot, and playing with Herc sure brings back memories. Just seeing the IBM message prefixes, and responding to console messages again was a wonderful bit of nostalgia! ”
— Bob Brown

“ Congratulations to you and your team on a fine piece of work! ”
— Rich Smrcina

“ Congratulations on a magnificent achievement! ”
— Mike Ross

“ It works even better than I imagined. Hercules is a fine piece of software! ”
— Dave Sienkiewicz

“ I have installed your absolutely fantastic /390 emulator. You won't believe what I felt when I saw the prompt. Congratulations, this is a terrific software. I really have not had such a fascinating and interesting time on my PC lately. ”
— Senior Systems Engineer

Read Moshe Bar's article about Hercules at

Read Richard Higson's chapter about Hercules in the IBM Redbook SG24-4987 Linux for S/390 at

View the foils from Jay Maynard's presentation given at SHARE Session 2880 in Minneapolis on Wednesday, 25 July 2001.

If you have any questions or comments, join the hercules-390 discussion group at

Bug reports (together with your diagnosis of the fault, please) may be sent to me, Jay Maynard, at jmaynard @

IBM, System/370, ESA/390, and z/Architecture are trademarks or registered trademarks of IBM Corporation. Other product names mentioned here are trademarks of other companies.

Last updated 8 July 2002