S/370 links

Here you will find more or less useful links to information about – or related to – the IBM 370 architecture Operating Systems, as well on the Hercules emulator. The Hercules emulator software emulates System/370 hardware on various computers / operating systems.

General info

Hercules 370 emulator

Helpful links

Operating Systems


The abbreviation stands for Multiple Virtual Storage.

JES2 Subsystem


VM stands for Virtual Machine. VM basically is a control program (CP) that allows the user to define and use several virtual machines on the same hardware.


MTS stand for Michigan Terminal System.


370 Assembler




Rexx is the de-facto scripting language on the mainframe, with implementations on z/VM, z/OS, MUSIC/SP and their predecessors. It originated as a one-man project of Michael F. Cowlishaw, starting in 1979 on VM. In CMS, Rexx became the followup language to EXEC and EXEC2. In VM/SP it was adopted as the official System Interpreter Product and it has been in all VM releases afterward. Around 1988 it appeared in MVS/TSO and alternative implementations on other platforms appeared.

VM/370 was the platform Rexx was initially developed on, but it never knew an official installation, as the product was passed around the VNET network in the early days. Pressure from customers, for example SLAC, lead to its status of official program product. REX, as the first releases were called, became REXX under pressure of IBM Legal; the department feared legal action by a competing, unrelated REX piece of software. In the modern VM/370 “Sixpack” distribution, BREXX (written in C) takes the place of the original, assembler written Rexx implementation.

Ray Mansell and Les Koehler are traditionally mentioned as the first users of Rexx. On VM, the combination of Rexx and Pipelines is particularly powerful.

In the 1990 Rexx was enhanced to support an object-oriented programming model, Object Rexx, designed by a team lead by Simon Nash. Implementations for TSO and VM were scrapped however, and the decision to open source the Linux (and Windows NT) version was postponed from 1995 to 2005; this was damaging to the uptake of the product. Open Object Rexx is maintained by The Rexx Language Association and has implementations for Windows, Linux and macOS. It also runs on AIX and Solaris.


non 370

IBM documentation

BREXX documentation