De facto standard
A de facto standard is a custom, convention, product, or system that has achieved a dominant position by public acceptance or market forces (such as early entrance to the market). De facto is a Latin phrase that means "concerning fact." De facto means "existing in fact," or "in practice but not necessarily ordained by law" or "in practice or actuality, but not officially established."
The term "de facto standard" is used in contrast with obligatory standards (also known as "de jure standards"); or to express the dominant voluntary standard, when there is more than one standard available for the same use.
In social sciences, a voluntary standard that is also a de facto standard is a typical solution to a coordination problem. The choice of a de facto standard tends to be stable in situations in which all parties can realize mutual gains, but only by making mutually consistent decisions. In contrast, an enforced "de jure standard" is a solution to the prisoner's problem.
A selection of well-known and illustrative examples of de facto and de jure standards:
- with consolidation by tradition of use:
- The driver's seat side in a given country starts as a user/industry preference, turning to a local tradition, then a traffic code local norm.
- The QWERTY system was one of several options for the layout of letters on typewriter (and later keyboard) keys. It was developed to prevent adjacent keys from jamming on early and later mechanical typewriters, often attributed to the typist's speed. It became a de facto standard because it was used on the most commercially successful early typewriters.
- The MP3 audio format started as an alternative to CD WAV (lossless format) for Internet music distribution, then replaced it — it is now supported by the vast majority of music players, audio transport, audio storage and noncommercial media. WAV and MP3 are also "de jure ISO formats".
- with consolidation by uniqueness and efficiency:
- HTML (computer file format) started as "de facto" (1993-1995) and became the "de jure" standard (1995-present-day).
- The PDF (computer file format) was first created in 1993 by Adobe. Adobe internal standards were part of its software quality systems, but they were neither published nor coordinated by a standards body. With the Acrobat Reader program available for free, and continued support of the format, PDF eventually became the de facto standard for printable web documents and e-books. In 2005, PDF/A became a de jure standard as ISO 19005-1:2005. As of 2007[update], PDF 1.7 is under development as ISO/DIS 32000.
Examples of long-time de facto but never de jure standards (for computer file formats):
- AutoCAD DXF: a de facto ASCII format for import and export of CAD drawings and fragments in the 1980s and 1990s. In the 2000s, XML based standards emerged as de facto standards.
- Microsoft Word DOC (over all other old PC word processors): one of the best known de facto standards. Due to the market dominance of Word, it is supported by all office applications that intend to compete with it, typically by reverse engineering the undocumented file format. Microsoft has repeatedly internally changed the file specification between versions of Word to suit their own needs, while continuing to reuse the same file extension identifier for different versions.
- The 1/2-inch (12.7 mm) spacing of the rollers in a bicycle chain.
- The IBM Personal Computer format, which used MS-DOS and Microsoft Windows operating systems, gained a large share of the personal computer market. Competing products like the Rainbow 100 were eventually withdrawn.
- Interpreted programming languages such as PHP that have multiple implementations tend to also have a de facto standard. In PHP's case the de facto standard is the binaries available from php.net, rather than the Phalanger implementation for example.
Standards battles 
- Alternating current over direct current: see War of Currents.
- VHS over Betamax (see videotape format war): when the VHS format for videotape recording was introduced, other recording formats were already available in the market. Regardless of whether Betamax was superior from a technical point of view or not, the VHS format won the format war due to superior marketing tactics by its proponents. The market could not support two competing formats; VHS became the de facto standard and Betamax was eventually withdrawn.
- Blu-ray Disc over HD DVD (see high definition optical disc format war).
Examples of standards that are "in dispute" for turns de facto:
- OASIS's OpenDocument format (a de facto standard for UNIX users (Apache OpenOffice, LibreOffice, Calligra, KOffice et al. use it as default file format) vs Microsoft's Office Open XML format (a de facto standard for MS-Windows users).
- Adobe Flash vs Scalable Vector Graphics (SVG), for vector graphics web page animations.
See also 
- thefreedictionary.com/de+facto adv; in fact, adj; existing in fact, whether legally recognized or not
- Edna Ullmann-Margalit: The Emergence of Norms, Oxford Un. Press, 1977. (or Clarendon Press 1978)
- ISO 19005-1:2005 - Document management - Electronic document file format for long-term preservation - Part 1: Use of PDF 1.4 (PDF/A-1)
- ISO/DIS 32000 - Document management - Portable document format - PDF 1.7
- Adobe - Release PDF for Industry Standardization FAQ