Fun things to do with your VM/370 CE machine – Fun with big computers

This is a hands-on introduction to exploring VM/370 Community Edition, an enhanced, community-maintained version of IBM’s VM/370 R6. It explains that CE adds many later fixes and features while still running within modest mainframe limits, and presents Docker or Podman as the easiest way to start an emulated system. Other options - running a nested virtual machine on an organizational mainframe or acquiring a physical machine - are possible but involve substantial practical hurdles. The guide also introduces 3270 terminals, whose form-based, screen-oriented interaction differs from scrolling terminals, and recommends x3270 for connecting to the system. It cautions against exposing an installation to the internet, particularly because the example user has a weak default password.

The practical examples walk through logging in to CMS, understanding the distinction between the control program and a user’s CMS virtual machine, and using CMS commands to inspect and edit files. Readers customize their PROFILE EXEC, then create and run a short BASIC “Hello World” program. A FORTRAN example shows how to list files, compile source, inspect the compiler’s listing and object output, and load the program for execution. The guide explains that FORTRAN’s output initially goes to a disk file rather than the terminal; FILEDEF can redirect it. It also highlights details of the environment, including case-insensitive commands, file names with separate name and type fields, PA2 paging, and the cryptic conventions around object files and output. The example ends with an unresolved missing first character in terminal output, illustrating how even simple tasks can expose old system quirks.