Write protection, (also known as record protection) is a mechanism that prevents erasure of valuable data by the accidental recording or storing of new data. The mechanism may be a switch, a sliding tab, a removable ring or a break-away tab. Data is protected if the tab is missing or the hatch window is open. Most commercial software, audio and video come pre-protected.

• Audio cassettes and VHS tapes have tabs on the rear edge that can be broken out.
• 8 mm and digital video tape cartridges have a sliding tab on the rear edge.
• 3-1/2 inch floppy disks have a sliding tab in a window on the right side. The tab can also be removed. (The window on the left side indicates a high density disk).
• 5-1/4 inch floppies have a notch on the right side that must be covered to protect the data.
• USB keys generally have a small switch.

When attempting to write to a protected floppy disk, the operating system will report a write protected error. By sliding the tab on a floppy or putting adhesive tape on a cassete, they become unprotected again. Write protection can also be implemented using digital rights management.

Write protection has a long history. IBM 1/2 inch magnetic tape reels, introduced in the 1950s, had a slot in the back around the hub. A soft plastic write protect ring had to be placed in the slot in order to write on the tape.