SimH

SimH, short for SIMulation of Historical Computers, is an open-source collection of computer simulators designed to emulate a wide range of vintage hardware. It enables users to run legacy operating systems and software on modern hosts, supporting education, preservation, and hobbyist exploration.

The project is a portable, multi-machine framework written in portable C and runs on Windows, macOS, and Unix-like systems. Its architecture is modular: each historic machine family is implemented as a separate simulator model, simulating CPUs, memory, and peripheral devices. A command-line monitor provides an interface to boot code, load media, configure devices, and manage I/O. SimH emphasizes accuracy, configurability, and extensibility, with new models contributed by volunteers.

SimH focuses on a broad family of DEC computers, including PDP-8, PDP-11, and VAX systems, and also supports several other historical platforms via additional modules. Users can install operating systems such as RT-11, TOPS-10, and various early UNIX variants to experience authentic environments.

Originating in the 1990s under the guidance of developer Bob Supnik, SimH has grown into a community-maintained project. It is released under a permissive open-source license and has been used by museums, educators, and enthusiasts to study and preserve computing history. The project is hosted on major code repositories, with GitHub serving as a current hub, and provides source code, documentation, and prebuilt binaries.