Pursuing Authenticity and Efficiency with Tape Images

The project's second stage, which began at the end of 2024, represented a strategic and philosophical shift. The motivation was not merely to escape the awkwardness of client-server file transfers, but to pursue an ideal vision: a complete Decwar PDP-10 system built from scratch using only SIMH tape images of original authentic DEC tapes. The ambition was to build TOPS-10 from DEC source tape using MONGEN (MONitor GENeration, analogous to building UNIX or Windows from source code), then install the appropriate DEC Fortran IV from DEC source tape (DEC FORTAN-10 V6), then install Decwar from reconstructed UT Austin SDT, build, and play.

The transition to a tape-based workflow marked a major jump up in efficiency and realism, with immediate and substantial improvements in cycle time and development ergonomics, rendering the Kermit-based approach obsolete for active development. The new process involved editing source files locally, creating a new SIMH tape image, an automated process taking less than a second, and simply restarting the SIMH PDP-10. The entire process, from end to end, takes a matter of seconds and is invoked with a single command or push of a button.

The new workflow was centered on SIMH tape images. The impact was profound, creating a much smoother and more flexible workflow. The paradigm shift was so complete that Kermit and client-server file transfer have completely vanished in practice and are retained as possibilities mostly for historical reasons, much like the possibility of using a terminal to perform interactive file editing on the PDP-10 using SOS or TECO. They’re possible and interesting historically, but not effective everyday workflows.

Beyond efficiency, this shift held deep cultural significance. By using the reconstructed SDT for every build, the project was "eating their own dog food." This practice is the ultimate validation of the archeological work, proving the integrity of the artifact by using it as the foundation for further progress. This also makes the entire process feel "super realistic". The technical elegance of this approach lies in its fidelity to the original hardware paradigm. The SIMH PDP-10 interacts with the tape image without awareness that it is not physical hardware. This commitment to authenticity is demonstrated in practice with every build from reconstructed SDT, ensuring a clean and consistent environment. While this Tape Era perfected the local build process, it remained tethered to a specific host machine's configuration, setting the stage for the next evolutionary step: total environment abstraction.