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

You can now run a classic mainframe operating system on your personal computer with minimal setup.

The VM/370 Community Edition (CE) is an enhanced, open-source version of IBM's classic VM/370 operating system. Users can easily set up and run VM/370 CE using Docker, with a command that launches a containerized mainframe environment accessible via a web-like 3270 terminal emulator. The article guides users through logging into the system as 'CMSUSER' with the password 'CMSUSER' and exploring basic CMS commands. It details how to customize the PROFILE EXEC script to alter the login experience and demonstrates running simple programs written in BASIC and FORTRAN, including compiling a FORTRAN program and examining its output files. The system runs on limited resources, typically a single CPU and 16MB of memory, and supports only open-source or public domain software.

The VM/370 CE represents a significant community effort to modernize and distribute a historically important operating system, akin to how Linux evolved from its early versions to modern distributions. Its accessibility via Docker makes it a practical tool for learning about mainframe computing, reverse engineering, or simply experiencing an emulation of a bygone era of computing. The system's limitations, such as single CPU and 16MB memory, are characteristic of its original architecture but are easily overcome by modern hardware, allowing for extensive experimentation.

The availability of VM/370 CE with open-source and public domain software facilitates direct engagement with its internal workings. The article's focus on practical tasks like customizing login scripts and compiling legacy languages such as BASIC and FORTRAN provides a hands-on learning experience. This accessibility democratizes access to mainframe operating system principles, which were previously confined to specialized hardware and expensive licenses, opening doors for educational purposes and retro-computing enthusiasts.