This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.
Platter systems are used commonly in `automated' booths, allowing one
projectionist to run several shows (such as in a multi-screen theater)
simultaneously by eliminating the need for manual changeovers and the
rewinding of reels. The platter itself is a large, flat, circular,
metal table, mounted on a column of like plates, on which the film is
wound, tails out, with the shipping reels all spliced together.
Platters are usually installed in stacks of three, allowing two films
to be ready to run at any one time, along with a takeup platter for
either. This setup also allows one print to be made up/broken down
while another is running.
 
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