Many of the great film noir movies were based on novels by the so-called “hardboiled” school of pulp writers, who told tales of cynical detectives, femme fatales, gangsters and gun molls in magazines like “Black Mask.” Some of the writers who began with the pulp magazines in the 1920s through the 1940s went on to write full-length novels in the same genre. In the 1950s and 1960s, another generation of hardboiled writers wrote exclusively for the cheap paperback market, and some of these books were later made into neo-noir movies- like 2010's “The Killer Inside Me,” based on the novel by Jim Thompson.
Is hardboiled the same as noir? Not exactly. Hardboiled crime fiction emphasizes gritty realism, violence and a pessimistic outlook, but it is often completely unsentimental. Noir adds an element of dark romanticism, a “gothic touch.” It's a difference in tone, and a slight one at that, but it could be characterized by saying that Tarantino's “Reservoir Dogs” is hardboiled (but not really noir) while “Memento” is a neo-noir. Both movies feature stories of crime and murder, corruption and mystery- but “Memento” has an element of romanticized pathos lacking in the straightforward violence of “Reservoir Dogs.”
Jim Thompson's novels are extremely hardboiled, without even a hint of sentiment. Raymond Chandler's detective fiction is definitely noir, with strong elements of romanticism. There's a distinction between the terms, but the overlap is so substantial that they are often used as if they were synonyms.