Page "Compact Cassette" Paragraph 24

All Compact Cassettes include a write protection mechanism to prevent re-recording and accidental erasure of important material.

Each side of the cassette has a plastic tab on the top that may be broken off, leaving a small indentation in the shell.

This indentation allows the entry of a sensing lever that prevents the operation of the recording function when the cassette is inserted into a cassette deck.

If the cassette is held with one of the labels facing the user and the tape opening at the bottom, the write-protect tab for the corresponding side is at the top-left.

Occasionally, manufacturers provided a movable panel that could be used to enable or disable write-protect on tapes.