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IBM tape reel with white write ring in place, and an extra yellow ring.

From top to bottom: an unprotected Type I cassette, an unprotected Type II, an unprotected Type IV, and a protected Type IV.

A sheet of 5+1⁄4" floppy disk write protect tabs.

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Write protection is any physical mechanism that prevents writing, modifying, or erasing data on a device. Most commercial software, audio and video on writeable media is write-protected when distributed.