Remember an old plus operator obsoleted by Google in 2011? In many search engines, including Google before October 2011, this operator is used to indicate a mandatory (or an important) keyword. Do you know when was the plus operator first used in an online search engine? I bet few would guess that it happened half a century ago, in the pre-Internet era:
In 1965, TEXTIR permitted users to do some search term weighting. By preceding a term with a plus sign, a searcher could direct TEXTIR to increase the score assigned of that word, and thus raise the score of the source document that contained that word.
How was the online search possible before Internet? One could use a phone line (and apparently a dial-up modem):
Queries were sent to SDC's Q-32 computer in Santa Monica via telephone from a Teletype Model 35 terminal ... In response, the system ... transmitted the texts of retrieved reports back by Teletype in relevance rank order.
Source: A History of Online Information Services 1963-1976 by C. P. Bourne and T.B. Hahn.
The online search service, one of the first of the kind, was developed and provided by the System Development Corporation (SDC). SDC is considered to be the first software company in the world.