How Everything Works
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Question 823

How long will the magnetic data last on a VCR tape before it becomes no longer useable as read data? — KR, Urbana, IL
As long as the tape is kept cool and dry, its magnetization should remain stable for years. However, there is the problem of magnetic imprinting from one layer of tape to the adjacent layers on a spool. With time, one layer transfers some of its magnetization to those adjacent layers. In a videotape, this imprinting leads to a gradual appearance of noise in the video images. As long as you're willing to tolerate a little video "snow," this imprinting shouldn't be too much of a problem. You can reduce its severity by occasionally winding and rewinding the tapes. But I don't see any real reason why a tape won't be reasonably useable for decades.

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