"... a terminate-and-stay-resident program (or TSR) was a computer program running under DOS that uses a system call to return control to DOS as though it has finished, but remains in computer memory so it can be reactivated later. Needless to say, this was extremely unreliable."
There were very likely some hacky TSRs that caused problems, but in my experience most were extremely reliable. We used an off-the-shelf TSR to enhance a motion control system that laser scribed ceramic vacuum checks for silicon wafer fabrication. Those things cost $5k in 1990, and took ~20h of processing, increasing their value to $15k; we wouldn't screw around with something that was inherently "extremely unreliable".
There were very likely some hacky TSRs that caused problems, but in my experience most were extremely reliable. We used an off-the-shelf TSR to enhance a motion control system that laser scribed ceramic vacuum checks for silicon wafer fabrication. Those things cost $5k in 1990, and took ~20h of processing, increasing their value to $15k; we wouldn't screw around with something that was inherently "extremely unreliable".