The 35mm motion picture film format became the standard around 1903. The reason is that it is the best size for avoiding grainy visuals - smaller film sizes blown up to screen dimensions actually show the existence of the chemical crystals on the film surface, i.e. grain. Early nitrate (nitrocellulose) film stock was dangerously flammable and was replaced by fireproof acetate for X-rays in 1933 and for motion pictures in 1951. (Kodak launched production of cellulose triacetate base motion picture film in 1948.)
Sony's launch of 'electronic cinematography' in the 1980s was not a success. Better camera technology brought 'digital cinematography' into wide use starting in 1998. Editing droids, 'green screen' stages, C.G.I., and distribution hardware and software followed. The major studios decreed in 2012 that they would no longer issue new films on physical 35mm film by end of 2013, and the commercial film labs began converting to digital operations.
Physical 35mm film projectors were replaced over 2012 and 2013 with 2K digital projection capabilities, which includes digital delivery by internet or satellite; only ten percent of U.S. motion picture theaters are keeping their 35mm projector hardware for showing of archival prints. (Archives like Library of Congress, MoMA, and U.C.L.A. are expected not to give up the 35mm technology.)
So the motion picture distribution industry is in transition: the business of film exchanges now serves only the art house market, film labs are digital, projection at your local movie theater is digital, and new projectionists need not be trained in 35mm technology. The general movie patron will not notice the difference, but the observant cineaste will find that certain features like depth, clarity, and color appear degraded.
Well, too bad. Progress happens. Film Is Dead, Long Live Digital.
{For folks without the backgroundL When a king of Britain dies, the traditional announcement takes the form of 'The King is dead, long live the King', which is a transfer of allegiance by the speaker to the successor.}