On the other hand, the IWERKS and IMAX platters are just the opposite. IMAX and IWERKS pull from the edge of the platter, and taken up on the center. However, there is a center ring in place even on the feed platter. Those platters can be looked at as a horizontally mounted reel-to-reel system. Even so, there is undoubtedly some kind of motor assist on feed-out because of the tremendous weight of the print. At the end of the presentation, 70mm IMAX and IWERKS must be rewound.

You can't really look at a conventional 35mm platter as a reel-to-reel system because the center ring is removed on feed-out. The 35mm system is said to be automatically rewinding as the movie runs. At the end of the show, just remove the center ring, re-thread, and start the next show.

With most reel-to-reel systems, the takeup reel is connected to the soundhead by means of a belt which drives the takeup clutch on the lower reel arm. Tension is adjustable, but does not remain constant throughout the entire reel. Some machines (e.g. the electronic Kinoton models) do have motor-driven takeup and provide constant takeup tension, but that is the exception rather than the norm.

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Then there is the MK2 reel unit that placed the 4 disks one above the other on two different angles to the post (looks more like a platter) and again it rewinds and uses a servo control
(Pictures of the MK2 under Ontario Science Centre)

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