[jes5199]

yeah, this author doesn’t know the history. Unix I/O was defined in opposition to practices in other OSes, that no longer exist

[guerrilla]

Clearly, since they barely know the system they are talking about but could you elaborate instead of leaving it vague? Which systems?

[jes5199]

there’s plenty of other comments that explain it, but, CP/M, VAX, teletypewriters, punch cards - all used in-band control characters rather than an external signal