The first PID system I did was in the 1980's on a mini-computer running FORTRAN and the RT11 OS. We has 7 PID loops, with sequencing and logging. We could control voltage, current, power, and temperature. One was designated the controlled variable and the others acted as limits. I created "stablity creiteria" which would include, open, heating, cooling, stable, conditionally, stable, heat up energy limit exceeded. The later would detect a shorted or misplaced thermocouple on heat-up. It was really, really cool.
It had the ability to create spreadsheet output (never implemented), but spreadsheets were not invented yet. The hook was there.
Basically we ran out of memory even with overlays. Software and true hardware thermocouples were not designed from the beginning because of some cost issues. The thermocouple modules had to be configured in groups of 4 and could be J,K, R or S. Ideally, the system should have handled a type "C" thermocouple. It was used for a long time for one part of the research process.
We wanted to run RSX-11 but management said no because we had no experience.
After we finished the "proof of concept" design, operators wrote programs in FORTRAN that would generate the TXT recipe files.
The was on a VT100 terminal of 80col x 25 lines.