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Concept
Write protection
Summary
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.
IBM -inch magnetic tape reels, introduced in the 1950s, had a circular groove on one side of the reel, into which a soft plastic ring had to be placed in order to write on the tape. ("No ring, no write.")
Audio cassettes and VHS videocassettes have tabs on the top/rear edge that can be broken off (uncovered = protected).
8 and -inch floppies can have, respectively, write-protect and write-enable notches on the right side (8-inch punched = protected; -inch covered/notch not present = protected). A common practice with single-sided floppies was to punch a second notch on the opposite side of the disk to enable use of both sides of the media, creating a flippy disk, so called because one originally had to flip the disk over to use the other side.
inch floppy disks have a sliding tab in a window on the right side (open = protected).
Iomega Zip disks were write-protected using the IomegaWare software.
Syquest EZ-drive (135 & 250 MB) disks were write-protected using a small metal switch on the rear of the disk at the bottom.
VHS-C, Video8, Hi8, and DV videocassettes have a sliding tab on the rear edge.
Iomega ditto tape cartridges had a small sliding tab on the top left hand corner on the front face of the cartridge.
USB flash drives sometimes have a small switch, though this has become uncommon. An example of a USB flash drive that supported write protection via a switch is the Transcend JetFlash series.
Secure Digital (SD) cards have a write-protect tab on the left side.
Extensively, media that, by means of design, can't operate outside from this mode: CD-R, DVD-R, Vinyl records, etc.
These mechanisms are intended to prevent only accidental data loss or attacks by computer viruses. A determined user can easily circumvent them either by covering a notch with adhesive tape or by creating one with a punch as appropriate, or sometimes by physically altering the media transport to ignore the write-protect mechanism.
Official source
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