Hercules Version 3: Frequently-Asked Questions

1.01What is Hercules?
1.02So what exactly does that mean?
1.03Is it functional enough to run production work?
1.04What are the licensing restrictions for Hercules?
2.01Can it run z/OS, z/VM, z/VSE?
2.02What operating systems can I run legally?
2.03What other programs will run under Hercules?
2.04Where can I obtain OS/360 ?
2.05Where can I obtain MVS ?
2.06Where can I obtain VM/370 ?
2.07Where can I obtain DOS/VS ?
2.08Where can I obtain Linux/390 ?
2.09Where can I find documentation?
3.01What PC hardware do I need to run Hercules?
3.02What sort of MIPS rate can I expect?
3.03What PC software do I need to run Hercules?
3.04What software do I need to build Hercules on Linux and Unix?
3.05What software do I need to build Hercules on Windows?
3.06Can Hercules be ported to run on other platforms?
4.01How can I create a virtual DASD volume?
4.02Can I read a tape which was created on a mainframe?
4.03Can I attach a PC tape drive to Hercules?
4.04Can I process mainframe tapes with Hercules?
4.05Can I create Assembler programs without a mainframe?
5.01What architectural features are implemented?
6.01Who are the Herculeans?
7.01Where can I obtain technical support?

1.01 What is Hercules?

Hercules is a software implementation of the System/370, ESA/390 and z/Architecture mainframe architectures. Hercules runs under Windows and Linux, as well as under various other Unix or Unix-like systems on Intel Pentium and other hardware platforms including Alpha, Sparc, and Mac.

1.02 So what exactly does that mean?

It means that your PC can execute programs designed to run on an IBM mainframe.

Hercules executes S/370, ESA/390, and z/Architecture instructions and channel programs. It emulates mainframe I/O devices by using PC devices. For example, 3390 DASD devices are emulated by large files on your hard disk, and local 3270 screens are emulated by tn3270 sessions.

Hercules implements only the raw S/370, ESA/390, and z/Architecture instruction set; it does not provide any operating system facilities. This means that you need to provide an operating system or standalone program which Hercules can load from an emulated disk or tape device. You will have to write the operating system or standalone program yourself, unless you can manage to obtain a license from IBM to run one of their operating systems on your PC, or use IBM programs and operating systems which are effectively in the public domain.

1.03 Is it functional enough to run production work?

Hercules has never claimed to be a production-capable system. It was always meant to be a system programmer's toy. Having said that, it's now become good enough to run a wide range of software without problems, and there are reports that it has been used to run production work in some parts of the world.

1.04 What are the licensing restrictions for Hercules?

Hercules is a copyright work which has been made generally available, subject to the terms of the Q Public License. In essence this allows free use and distribution of the program for personal and commercial use. You may not distribute modified copies of the program, but you may distribute your own patches along with the program, provided that you also grant the maintainer permission to include those patches in future versions of the program. You may not copy any portion of the source code for use in any other program.

2.01 Can it run z/OS, z/VM, z/VSE?

Yes. Hercules is a software implementation of z/Architecture, and so it is capable of running z/OS, z/VM, and z/VSE. Hercules also implements ESA/390 (including SIE) and so it can run OS/390, VM/ESA, and VSE/ESA, as well as older versions of these operating systems such as MVS/ESA, MVS/XA, MVS/SP, MVS/SE, VM/SP, VSE/SP, and DOS/VSE.

But (and this is a big but), these operating systems are all IBM Licensed Program Products, whose conditions of use generally restrict their usage to specific IBM machine serial numbers. So you cannot just copy these systems from work and run them on your PC, as this would almost certainly be a violation of your company's licensing agreement with IBM.

2.02 What operating systems can I run legally?

Operating systems which may legally be run on Hercules include:

2.03 What other programs will run under Hercules?

Any program which uses the S/370, ESA/390, or z/Architecture instruction set, as implemented in Hercules. Some special utilities in the form of standalone programs are known to run well. A good example is Jan Jaeger's excellent standalone editor (ZZSA) which is included in the Hercules distribution, or it can be downloaded from http://www.cbttape.org/~jjaeger; ZZSA allows you to examine and edit MVS datasets without the need to load an operating system. Note: ZZSA runs in ESA/390 mode. See Jan Jaeger's website for more information and special logon procedures.

2.04 Where can I obtain OS/360 ?

Jay Maynard's "IBM Public Domain Software Collection" at http://www.ibiblio.org/jmaynard/ contains copies of the OS/360 Release 21.8 distribution tapes.

2.05 Where can I obtain MVS 3.8 ?

The MVS 3.8J Turnkey System built by Volker Bandke can be obtained from http://www.bsp-gmbh.com/

For news about updates to the MVS 3.8J Turnkey System, subscribe to the H390-MVS forum at http://tech.groups.yahoo.com/group/H390-MVS/

Juergen Winkelmann has made available an updated MVS Turnkey System which can be downloaded from http://wotho.ethz.ch/tk4-/

Paul Edwards created a distribution consisting of a modified version of Hercules together with operating system modifications which allow applications to break the 24-bit addressing barrier inherent in S/370. The distribution is called MVS/380 and it can be downloaded from http://mvs380.sourceforge.net/

2.05 Where can I obtain VM/370 ?

The VM/370 page at http://www.cbttape.org/vm6.htm contains download links for the Andy Norrie VM 4-pack system and the Bob Abeles VM/370 R6 distribution.

Dave Wade's VM/370 Downloads page at http://www.smrcc.org.uk/members/g4ugm/VM370.htm contains links to the most recent VM/370 distributions.

You may also wish to subscribe to the H390-VM forum at http://tech.groups.yahoo.com/group/H390-VM/

2.07 Where can I obtain DOS/VS ?

George Shedlock's DOS/VS 5-pack system can be obtained from https://docs.google.com/open?id=0B7scZ2voEa--Zm50U09xYy15ejg

Other useful files may be downloaded from the H390-DOSVS forum at http://tech.groups.yahoo.com/group/H390-DOSVS/files/

2.08 Where can I obtain Linux/390 ?

The best starting point for information about Linux for S/390 and Linux for zSeries is http://www.linuxvm.org/

2.09 Where can I find documentation?

There are several sites containing introductory documentation for MVS 3.8 with Hercules, including:

Much of the original IBM documentation for the 360 and 370 series is preserved at the bitsavers.org website. A good starting point is:

Jay Maynard produced a document describing how to build an OS/360 system on Hercules, called "OS/360 on Hercules". It can be found at

This will build an MVT system without TCAM/TSO, but with two 3270 consoles. You will need Malcolm Beattie's "Guide to Using 3270 Consoles and Terminals for Hercules" with this MVT version.

3.01 What PC hardware do I need to run Hercules?

Classic IBM operating systems (OS/360, MVS 3.8, VM/370) are very light by today's standards and will run satisfactorily on a 300Mhz Pentium with as little as 32MB RAM.

Anything more up-to-date, such as Linux/390 or OS/390, requires much more processing power. Hercules is CPU intensive, so you will want to use the fastest processor you can get. A 2GHz Pentium, preferably with hyperthreading, will probably provide acceptable performance for a light workload. Recent 64-bit multiprocessor systems will provide better performance. Hercules makes extensive use of multi-threading to overlap I/O with CPU activity, and to dispatch multiple emulated CPU's in parallel.

For the latest 64-bit operating systems such as zLinux and z/OS, be aware that there is a performance penalty when Hercules emulates z/Architecture on a 32-bit processor such as the Pentium. If you are serious about running 64-bit then you will probably want to build Hercules for a 64-bit processor such as Alpha (DEC/Compaq/HP), AMD64 (AMD Opteron, Athlon-64, Turion 64), IA64 (Intel Itanium 2), together with a 64-bit version of Linux, or PPC (Power Mac G5) with OS X.

Hercules does not depend on the x86 architecture. It has been built and run successfully on 500 MHz Alpha 21164, SPARC, and S/390 Linux. One guy has even run OS/360 under Hercules under Linux/390 under Hercules under Linux/390 under VM/ESA! The prize for the world's smallest mainframe probably goes to Ivan Warren, who claims to have run VM/370 under Hercules on an iPAQ 5450 handheld PDA.

You should provide enough RAM to accommodate your S/390 real storage (main storage plus expanded storage) in addition to the normal requirements of your PC's operating system. For maximum throughput, you should set your main and expanded storage sizes high enough to eliminate S/390 paging. S/390 storage is allocated out of your PC's virtual storage.

You also need enough hard disk space to accommodate the emulated DASD. A virtual "3330 model 1" disk drive will need about 100 megabytes of space for emulation (a 3330-11 will need about 200 megabytes). A 3380 "single density" model will need about 650MB, a 3390 model 2 needs about 2GB, and a 3390 model 3 needs about 3GB. If you use the compressed CKD DASD feature, these sizes will shrink dramatically, usually to about 20 to 30 percent of the original size.

3.02 What sort of MIPS rate can I expect?

Thanks to the cumulative work of many individuals, including Valery Pogonchenko, Juergen Dobrinski, Albert Louw, Gabor Hoffer, Jan Jaeger, Paul Leisy, Clem Clarke, and Greg Smith, the performance of Hercules today is vastly better than it was 5 years ago.

Even on a Celeron 300 you should see an execution speed of 1 to 2 MIPS, which is enough to run OS/360 (MFT or MVT) or MVS 3.8 with a response time better than that of a 3033 from the 1970's. It's also fast enough to run VSE/ESA with an acceptable response time. On a more recent system with a 2GHz Pentium processor, you may see the system peak at around 30 MIPS which is enough to run Linux/390 or z/OS with a light workload.

Performance on server class machines is now fairly respectable. For example, on a dual-core Intel Xeon with hyperthreading (4 CPUs) running at 3.46GHz, you might expect to see a sustained MIPS rate of 40 to 60 MIPS. A dual-processor quad-core Mac Pro (8 cores, 3 GHz) will sustain over 150 MIPS. For anyone who is prepared to spend a considerable amount of money on their Hercules system, there are reports that a sustained 300+ MIPS has been achieved on an Intel Core i7 processor running at 3.75GHz using all four cores plus hyperthreading (8 CPUs).

Typical I/O rates of around 50 EXCP/second are reported on average hardware, with rates over 500/second achievable with hardware RAID.

3.03 What PC software do I need to run Hercules?

The following software platforms are supported:

  • Linux (kernel 2.4 or later)
  • Windows XP, Windows Vista, or Windows 7
  • Mac OS X 10.3 or later
  • Solaris 2.9 or later (Sparc or Intel)
  • FreeBSD

    You will also need tn3270 client software for the virtual 3270 console. The tn3270 client can run on the same machine as Hercules, or on any Unix or Windows box with a TCP/IP connection to the Hercules machine.

    The supported and recommended tn3270 clients for Hercules are:

    x3270 for Unix
    x3270 is included with most Linux distributions, or you can download it from http://x3270.bgp.nu/
    Vista tn3270 for Windows
    Vista tn3270 can be obtained from www.tombrennansoftware.com. The very modest license fee charged for this excellent 3270 emulator helps to support an independent software developer.
    Brown University tn3270 for Macintosh
    Brown University tn3270 is freely available. You can download it from http://www.brown.edu/cis/tn3270/. There is one setting that must be changed to use this program with some operating systems, especially MVS 3.8: Open a connection to Hercules, but before IPLing the system, go to the Session->Features menu and set "Change embedded nulls to blanks" to "No". Click on "OK". Now, click on File->Save default settings... to make the setting permanent.

    Other tn3270 clients, such as QWS3270, IBM Personal Communications, Attachmate Extra, or Dynacomm Elite should also work in most cases, but be aware that some tn3270 clients have bugs which make them unusable as OS/360 or MVS consoles.

    3.04 What software do I need to build Hercules on Linux and Unix?

    To build Hercules for Linux and other Unix-like environments you need to use the gcc compiler, version 3.x or above. You will also need a full set of GNU development tools, including recent versions of autoconf, automake, libiconv, make, perl, sed, and m4. Refer to the util/bldlvlck file in the Hercules distribution for details.

    3.05 What software do I need to build Hercules on Windows?

    To build Hercules for the Windows environment you need to use the Microsoft C/C++ compiler (MSVC) version 14.x or later. The 32-bit compiler and SDK are packaged as Microsoft Visual C++ 2010 Express (Version 16.x) available for download from Microsoft.

    Although no longer available for download, Microsoft Visual C++ 2005 Express (Version 14.x) or Microsoft Visual C++ 2008 Express (Version 15.x) may also be used. Alternatively, Microsoft Visual Studio 8.0, 9.0, or 10.0 may be used. For further information, see the README.WIN32 file.

    To build Hercules for 64-bit Windows platforms you will need either Microsoft Visual C++ 2010 Express and the Microsoft Windows SDK 7.1, or Microsoft Visual Studio 9.0 or 10.0 Professional. For further information, see the README.WIN64 file.

    3.06 Can Hercules be ported to run on other platforms?

    With the introduction of autotools, we do make efforts to ensure Hercules builds and run on several different operating system platforms (mostly Linux, Windows, MAC, Solaris, and FreeBSD right now), but we of course simply cannot guarantee that it will run on every operating system platform out there.

    The Hercules code is not intended to be specific to Intel hardware, so if you find any issues or faults related to running on other hardware (SPARC, Alpha, PPC, ...) under Linux, feel free to report it to the Hercules forum (see the Hercules Technical Support page).

    4.01 How can I create a virtual DASD volume?

    The Creating Hercules DASD document describes various methods of creating and loading virtual DASD volumes.

    4.02 Can I read a tape which was created on a mainframe?

    Yes, indirectly. The mainframe tape must be converted to AWSTAPE format and then downloaded to your PC. The tapeconv.jcl file in the Hercules directory contains a sample program which you can run under OS/390 on your mainframe system. It reads a file from tape and converts it to AWSTAPE format. Download the AWSTAPE file to your PC (making sure to choose binary format for the download), and then add the downloaded filename to the Hercules configuration file as a virtual tape device. You will then be able to read the tape file from the virtual tape drive located on your PC.

    Note: the "tapeconv" program will not correctly process input tapes whose block size exceeds 32760! One symptom of this may be the message " ADRY011E I/O ERROR - DEVICE NOT ATTACHED.0000,NA,00...00,0000" when attempting to restore from tape originally created using the default DF/DSS block size. The solution is to recreate the dump tape with DCB=BLKSIZE=32760.

    4.03 Can I attach a PC tape drive to Hercules?

    Yes. Hercules can read and write tapes on SCSI drives. I have tested this with 4mm DAT, QIC-1000, and 9-track drives.

    4.04 Can I process mainframe tapes with Hercules?

    Yes. It is possible to obtain 9-track open reel drives and 3480-type cartridge drives which attach to the SCSI bus. Hercules makes these appear to the operating system as channel-attached 3420 or 3480 devices, making it possible to read and write real mainframe tapes.

    4.05 Can I create Assembler programs without a mainframe?

    Yes. If you want to write Assembler (BAL) programs to run on Hercules, but you don't have access to a mainframe, then there are two interesting products which you can run on your PC to assemble programs:

    The "Tachyon 390 Cross Assembler" ( http://www.tachyonsoft.com/tachyon )
    With this assembler you can produce S/390-compatible object decks using your Linux or Windows PC. A high degree of HLASM compatibility, coupled with the ability to perform complex assemblies at lightning speed, make this a product which is well worth looking at. I have tried this assembler and it is truly amazing.
    The "Dignus Systems/C Compiler" ( http://www.dignus.com )
    This is a C compiler which runs under Windows or Linux and generates mainframe assembler code which you can then assemble using the Tachyon assembler.

    Sam Golob wrote a fascinating review of these two products in the September 1999 issue of NaSPA Technical Support magazine.

    5.01 What architectural features are implemented?

    The following standard features of ESA/390 have been implemented:

    The following optional features of ESA/390 have been implemented:

    The following optional features of z/Architecture have been implemented:

    The following optional features of z/Architecture have not yet been implemented:

    The following standard feature has not yet been implemented:

    The following optional features have been partially implemented:

    The following features are not yet implemented, either due to lack of documentation, limited host system capability, or lack of supporting hardware:

    Hercules is compliant with IBM's ALS-1, ALS-2 and ALS-3 architectural level sets to the degree necessary to run all OS/390 versions through 2.10 and known versions of z/OS in both ARCHLVL 1 and ARCHLVL 2 mode, and Linux and z/VM in both ESA/390 and z/Architecture mode.

    6.01 Who are the Herculeans?

    The following people are among those who have contributed to this project, either as coders or as testers or both:

  • Roger Bowler (original author)
  • Jay Maynard
  • Jan Jaeger
  • Butch Anton
  • Volker Bandke
  • David Barth
  • Shelby Beach
  • Malcolm Beattie
  • Mario Bezzi
  • Florian Bilek
  • Gordon Bonorchis
  • Gert Caers
  • Mike Cairns
  • Bill Carlborg
  • Chris Cheney
  • Marcin Cieslak
  • Clem Clarke
  • Peter Coghlan
  • Vic Cross
  • Jacob Dekel
  • Guy Desbiens
  • Jacques Dilbert
  • Juergen Dobrinski
  • Fritz Elfert
  • Neale Ferguson
  • Tomas Fott
  • Mike Frysinger
  • Martin Gasparovic
  • Mark Gaubatz
  • Steve Gay
  • Paolo Giacobbis
  • Peter Glanzmann
  • Roland Goetschi
  • Graham Goodwin
  • Paul Gorlinsky
  • Harold Grovesteen
  • John P. Hartmann
  • Glen Herrmannsfeldt
  • Brandon Hill
  • Laddie Hanus
  • Robert Hodge
  • Gabor Hoffer
  • Dan Horak
  • Peter J. Jansen
  • Soren Jorvang
  • Willem Konynenberg
  • John Kozak
  • Nobumichi Kozawa
  • Peter Kuschnerus
  • Paul Leisy
  • Kevin Leonard
  • Albert Louw
  • Peter Macdonald
  • Lutz Mader
  • Tomas Masek
  • Rick McKelvy
  • John McKown
  • Dave Morton
  • Christophe Nillon
  • Mike Noel
  • Andy Norrie
  • Dutch Owen
  • Max H. Parke
  • Gerd Petermann
  • Reed H. Petty
  • Jim Pierson
  • Richard Pinion
  • Tim Pinkawa
  • Pasi Pirhonen
  • Valery Pogonchenko
  • Andy Polyakov
  • Frans Pop
  • Wolfhard Reimer
  • Emerson Santos
  • Jeff Savit
  • Axel Schwarzer
  • Paul Scott
  • Daniel Seagraves
  • Victor Shkamerda
  • Ian Shorter
  • Greg Smith
  • Enrico Sorichetti
  • John Summerfield
  • Peter Sylvester
  • Mark Szlaga
  • Adam Thornton
  • Adrian Trenkwalder
  • "Fish" (David B. Trout)
  • Ronen Tzur
  • Bernard van der Helm
  • Ard van der Leeuw
  • Kris Van Hees
  • Adam Vandenberg
  • Christophe Varlet
  • Kees Verruijt
  • Giuseppe Vitillaro
  • Dave Wade
  • Ivan Warren
  • Juergen Winkelmann
  • Ian Worthington
  • Rod Zazubek
  • Bjoern A. Zeeb
  • Matt Zimmerman

    And thanks for support and encouragement from:

  • Tim Alpaerts
  • Bertus Bekker
  • Giorgio de Nunzio
  • Rick Fochtman
  • Alex Friis
  • Sam Golob
  • Achim Haag
  • Cory Hamasaki
  • Tony Harminc
  • Richard Higson
  • Jim Keohane
  • Sam Knutson
  • Mike Ross
  • Daniel Rudin
  • Rich Smrcina
  • Henk Stegeman
  • Mark S. Waterbury

    If anyone feels they have been unfairly omitted from either of these lists, please let the maintainer (maintainer @ hercules-390.eu) know.

    7.01 Where can I obtain technical support?

    Please see the Hercules Technical Support page.


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