As far as I understand it, embedded software is just software (that runs on a general purpose CPU) that has little if any user input or configuration. Embedded software powers IP routers, cars, computer mice, etc.
My question is: When (roughly) was the historical moment when embedded software was first considered cost-effective for some applications (rather than an equal technical solution not involving embedded software)? Which applications and why?
Detail: Obviously there is a tradeoff between the cost of a CPU fast enough to perform X in software versus the cost of designing hardware that performs X.