The Free On-line Dictionary of Computing (30 December 2018):
(vi) /V-I/, /vi:/, *never* /siks/ A screen
editorcrufted together by Bill Joy for an early BSD
release. vi became the de facto standard Unix editor and a
nearly undisputed hacker favourite outside of MIT until the
rise of Emacs after about 1984.
It tends to frustrate new users no end, as it will neither
take commands while expecting input text nor vice versa, and
the default setup provides no indication of which mode the
editor is in (one correspondent accordingly reports that he
has often heard the editor's name pronounced /vi:l/).
Nevertheless it is still widely used (about half the
respondents in a 1991 Usenet poll preferred it), and even
some Emacs fans resort to it as a mail editor and for small
editing jobs (mainly because it starts up faster than the
bulkier versions of Emacs).
See holy wars.