Alongside the write-protect hole were two that were never used.
The diagram to the right shows a green sliding write-protect tab in both the unlocked and locked positions.
Generally, it is possible to write-protect some selected parts (as video clips) to prevent erasure.
Unlike 5-inch or 3-inch disks, the 3-inch disks were designed to be reversible and sported two independent write-protect switches.
To solve this problem, a user could cover the square hole with a piece of tape "opposite" the write-protect tab, and re-insert the disk.
Each side has its own independent write-protect switch.
