The PDP-6 monitor, and its PDP-10 successor TOPS-10, used control-Z (SUB) as an end-of-file indication for input from a terminal.
ðə pˌiːdˌiːpˈiː sˈɪks mˈɑːnɪɾɚ, ænd ɪts pˌiːdˌiːpˈiː tˈɛn səksˈɛsɚ tˈɑːps tˈɛn, jˈuːzd kəntɹˈoʊlzˈiː ˌɛsjˌuːbˈiː æz ɐn ˈɛndʌvfˈaɪl ˌɪndɪkˈeɪʃən fɔːɹ ˈɪnpʊt fɹʌm ɐ tˈɜːmɪnəl.