Write protection is any physical mechanism that prevents modification or erasure of valuable data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 on a device. Most commercial software, audio and video is sold pre-protected.

Examples

• IBM
  IBM
  International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
  
   1/2 inch magnetic tape
  Magnetic tape
  Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
  
   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
  VHS
  The Video Home System is a consumer-level analog recording videocassette standard developed by Victor Company of Japan ....
  
   videocassettes have tabs on the top/rear edge that can be broken off (uncovered = protected).
• 8 and 5¼ inch floppies can have, respectively, write-protect and write-enable notches on the right side (8″: punched = protected; 5¼″: covered/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
  Flippy disk
  A flippy disk is a double-sided 5¼" floppy disk, specially modified so that the two sides can be used independently in single-sided drives...
  
  , so called because one originally had to flip the disk over to use the other side.
• 3½ inch floppy disk
  Floppy disk
  A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
  
  s have a sliding tab in a window on the right side (open = protected).
• Iomega
  Iomega
  Iomega is an American producer of consumer external, portable and networking storage hardware. Established in the 1980s, Iomega has sold more than 410 million digital storage drives and disks. On April 8, 2008, EMC Corporation announced its plans to acquire Iomega for a consideration of US $213M...
  
   Zip disks were write protected using the IomegaWare software.
• Syquest EZ-drive (135 & 250MB) disks were write protected using a small metal switch on the rear of the disk at the bottom.
• 8mm, Hi8, and DV
  DV
  DV is a format for the digital recording and playing back of digital video. The DV codec was launched in 1995 with joint efforts of leading producers of video camcorders....
  
   videocassettes have a sliding tab on the rear edge.
• Iomega
  Iomega
  Iomega is an American producer of consumer external, portable and networking storage hardware. Established in the 1980s, Iomega has sold more than 410 million digital storage drives and disks. On April 8, 2008, EMC Corporation announced its plans to acquire Iomega for a consideration of US $213M...
  
   ditto
  Ditto drive
  The Ditto Drive series was a proprietary magnetic tape data storage system released by Iomega during the 1990s. It was marketed as a backup device for personal computers....
  
   tape cartridges had a small sliding tab on the top left hand corner on the front face of the cartridge.
• USB flash drive
  USB flash drive
  A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...
  
  s and most other forms of solid state storage sometimes have a small switch.
• Secure Digital
  Secure Digital
  Secure Digital is a non-volatile memory card format developed by the SD Card Association for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.Secure Digital...
  
   (SD) cards have a write-protect tab on the left side.

These mechanisms are intended to prevent only accidental data loss or attacks by computer virus

Computer virus

A computer virus is a computer program that can replicate itself and spread from one computer to another. The term "virus" is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability...

es. A determined user can easily circumvent them either by covering a notch with adhesive tape

Adhesive tape

Adhesive tape is one of many varieties of backing materials coated with an adhesive. Several types of adhesives can be used.-Types:Pressure sensitive tape...

 or by creating one with a punch

Hole punch

A hole punch is a common office tool that is used to create holes in sheets of paper, often for the purpose of collecting the sheets in a binder or folder.The origins of the hole punch date back to Germany via Matthias Theel, where two early patents for a...

 as appropriate, or sometimes by physically altering the media transport to ignore the write-protect mechanism.

Write-protection is typically enforced by the hardware. In the case of computer devices, attempting to violate it will return an error to the operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 while some tape recorders physically lock the record button when a write-protected cassette is present.

Write blocking

Write blocking, a subset of write protection, is a technique used in computer forensics

Computer forensics

Computer forensics is a branch of digital forensic science pertaining to legal evidence found in computers and digital storage media...

 in order to maintain the integrity of data storage devices. By preventing all write operations to the device, e.g. a hard drive, it can be ensured that the device remains unaltered by data recovery methods.

Hardware write blocking was invented by Mark Menz and Steve Bress (US patent 6,813,682 and EU patent EP1,342,145)

Both hardware and software write-blocking methods are used; however software blocking is generally not as reliable.