Micro Mainframe
MVS and OS/390

In 1989 I discovered the PC/370 program, written by Don Higgins.  It allows programs written in mainframe Assembler to be assembled, executed, and debugged on a microcomputer.  It was placed in the public domain by the author and eventually became the basis for Merant's Assembler workbench product.  As someone who has for years had a dream of having a small mainframe computer to play with at home, this was a good first step to realizing that dream.

In the decades since, there have been other options toward that dream, but most of them are either as expensive as trying to install a mainframe or just too limited to be a realistic solution.

Early in 2000, I discovered Hercules.  Hercules is a software implementation of S/370 and ESA/390 which runs under Linux or Windows on a personal computer.  The Hercules software executes S/370, ESA/390, and z/OS 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 the PC hard disk, and local 3270 screens are emulated by tn3270 sessions. 

Hercules is not a commercial product.  In fact, Roger Bowler, the author and originator of Hercules expressly prohibits commercial use of the program.  Presently, a number of people from around the world are contributing to the ongoing development of Hercules and extending its capabilities.  In February, 2002, the 2000th member joined the main Hercules' discussion group.  Some of these people have never had access to an IBM mainframe, so Hercules is literally introducing new people to S/370 hardware, operating systems, and management concepts.

At the present time, Hercules is capable of running MVS 3.8, VM, OS/360, DOS/VS and Linux/390, as well as some stand-alone utility programs.  In addition, VTAM, TCAM and TSO have been successfully genned and enabled.  All of the language compilers and utilities included with MVT have been proven to work correctly.  Members have been adept at retrieving additional language compilers developed at universities and private companies from archives.  As members discover and implement "third party" software, it is made available through the group archives and web sites.

At the time I write this, there are over 5,000 members of the main Hercules discussion group, and there are also discussion groups for the various operating systems being run under Hercules.  The requirements to run Hercules are easily met and there are step-by-step guides available to help you through the process of installing the emulator and a target operating systems.  You can also order a "turnkey" CD-ROM that will install the entire system on your computer in a matter of minutes, simply by answering a few questions.

For more information about Hercules, to view my contributions to the Hercules New Users Documentation Effort, and to download software that can be run under Hercules/MVS, visit my Hercules page.

This page was last updated on July 31, 2008.