Operating Systems Status
Hercules is technically compatible with all IBM mainframe operating systems, even older versions which no longer run on newer mainframes. However, many mainframe operating systems require vendor licenses to run legally. Older IBM operating systems including OS/360, DOS/360, DOS/VS, MVS, VM/370, and TSS/370 are either public domain or "copyrighted software provided without charge." Newer licensed operating systems, such as OS/390, z/OS, VSE/ESA, z/VSE, VM/ESA, z/VM, TPF/ESA, and z/TPF are technically compatible but cannot legally run on the Hercules emulator except in very limited circumstances, and they must always be licensed from IBM. IBM's Coupling Facility control code, which enables Parallel Sysplex, and UTS also require licenses to run.
The MUSIC/SP operating system may be available for educational and demonstration purposes upon request to its copyright holder, McGill University. Some of MUSIC/SP's features, notably networking, require z/VM (and thus an IBM license). However, a complete demonstration version of MUSIC/SP, packaged with the alternative Sim390 mainframe emulator, is available.
There is no known legal restriction that inhibits running the open source operating systems Linux on System z and OpenSolaris for System z on the Hercules emulator. They run well on Hercules, and many Linux on System z developers do their work using Hercules. Several distributors provide 64-bit z/Architecture versions of Linux, and some also provide ESA/390-compatible versions. Mainframe Linux distributions include SUSE Linux Enterprise Server, Red Hat Enterprise Linux, Debian GNU/Linux, CentOS, and Slackware. Sine Nomine Associates brought OpenSolaris to System z, relying on features provided by z/VM. Emulation of those specific z/VM features for OpenSolaris is included starting with Hercules Version 3.07. Certain unencumbered editors and utilities which can run on a mainframe without a parent operating system may be available to run on Hercules as well.
Hercules can be used as a development environment to verify that code is portable (across Linux processor architectures, for example), supports symmetric multiprocessing (SMP), and is 64-bit "clean." There is also a large community of current and former mainframe operators and programmers, as well as those with no prior experience, who use Hercules and the public domain IBM operating systems as a hobby and for learning purposes. Most of the skills acquired when exploring classic IBM mainframe operating system versions are still relevant when transitioning to licensed IBM machines running the latest versions.
The open source nature of Hercules means that anyone can produce their own customized version of the emulator. For example, a group of developers independent of the Hercules project implemented a hybrid mainframe architecture which they dubbed "S/380" using modifications to both Hercules and to freely available classic versions of MVS, enhancing the latter with some degree of 31-bit binary compatibility with later operating system versions.
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