DSEE for reproducible builds

The reproducible build idea was part of the Domain Software Engineering Environment" (DSEE; pronounced "dizzy") which was offered by Apollo Computer Inc around the 1980s and 1990s: thirty to forty years ago. (Apollo Computer and Sun Microsystems were serious competitors in some markets.) Each software component had a Makefile which specified all the tools and versions that were used to build it, and the result of each build contained a unique identifier for that build. Each tool also had such a Makefile (recursively), and the version control system for source code and built components contained the complete history of all components that ever existed. The operating system guaranteed that enough machinery existed to re-create any build in the entire history, using the specified version of each tool at each step. A typical build farm used dozens to hundreds of machines connected by 400MHz token-ring cabling (circular full duplex daisy chain.) It was a chore to keep every machine running during a build of the entire system, which might take several days depending on which point-in-time was chosen to be the epoch.