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The first version of PRONOM was developed by The National Archives digital preservation department in March 2002. Its genesis lies in the need to have ready access to reliable technical information about the nature of the electronic records now being stored in our Digital Archive.

By definition, electronic records are not inherently human-readable. File formats encode information into a form which can only be processed and rendered comprehensible by very specific combinations of hardware and software. The accessibility of that information is therefore highly vulnerable in today’s rapidly evolving technological environment. This issue is not solely the concern of digital archivists, but of all those responsible for managing and sustaining access to electronic records over even relatively short timescales.

Technical information about the structure of those file formats, and the software products which support them, is therefore a prerequisite for any digital preservation regime. PRONOM was developed to provide this, initially as an internal resource for The National Archives’ staff, but later made publicly available for anyone to use.

PRONOM 2 was released in December 2002, and provided support for the development of multi-lingual versions of the system, through the replacement of field tags. The web-enabling of PRONOM (PRONOM 3) in February 2004 represented the starting point for the development of PRONOM as a major online resource for the international digital preservation community.

Since that time, considerable effort has been devoted to the development of PRONOM’s content. The initial dataset has now grown to incorporate over 1,300 individual file format entries, and work is ongoing to improve the information and coverage of file formats in the registry.

PRONOM has undergone a number of development phases since the initial version release. The current version is PRONOM 6.2, and further developments are in the pipeline.

The development of PRONOM 3 was made possible by the generous support of a number of organisations and individuals. Please see our acknowledgements list

Users of PRONOM may be interested in related international projects.

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Work has been undertaken to create a linked data version of PRONOM. We hope to revisit this model for PRONOM in the future. As part of a broad reorganisation of The National Archives web services the current iteration of Linked Data PRONOM has been removed.

Preservation Planning

The National Archives’ long-term preservation strategy is based on object migration, coupled with retention of all records in their original formats. PRONOM was initially developed to support this work, and focused on the development of migration pathways for the automatic conversion of electronic records to new formats as required for preservation or presentation purposes.

PRONOM records information about file formats and the product support lifecycle for the software tools required to create or render them. This information will play a vital role in making decisions about when to migrate. In addition, existing information about the formats that particular software can read and write can form the basis for identifying potential migration pathways.

PRONOM Unique Identifiers

The National Archives developed and implemented an extensible scheme of PRONOM Unique Identifiers (PUIDs), which provide persistent, unique, and unambiguous identifiers for file formats. Such identifiers are fundamental to the exchange and management of electronic objects, by allowing human or automated user agents to unambiguously identify, and share the identification of, the encoding format of an object. This is a virtue both of the inherent uniqueness of the identifier and of its binding to a definitive description of the format in a file format registry, such as PRONOM. No existing, universally-applicable system provides for this.

UNIX "magic numbers" and Macintosh data-forks do provide some of this functionality, but the same is not true within Microsoft DOS or Windows environments. The three-character file extension is neither standardised nor unique and is interpreted differently by different environments. Equally, the IANA MIME-type scheme does not provide sufficient granularity or coverage to satisfy the requirements for unique identifiers. The PUID scheme was developed for the single purpose of providing such identifiers.

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New information

We maintain a continual programme to enhance the content of PRONOM with new information. We are working to develop relationships with various stakeholders active in this area, in order to share this important information with the digital preservation community and wider public.

If you would like to assist with this work by submitting information, please use the online submission form . If you have comments on any existing information, or suggestions for other information which you would like to see included, please contact us .


The following documents are available to download:

PDFPDF document, opens in a new window (174 Kb) | RTFRTF document, opens in a new window (1.5 Mb)

PRONOM 4 user requirements PDFPDF document, opens in a new window (320 Kb) | RTFRTF document, opens in a new window (313kb)

PRONOM 4 information model PDFPDF document, opens in a new window (744 Kb) | RTFRTF document, opens in a new window (9.28 Mb)

DROID API documentation PDFPDF document, opens in a new window (289 Kb) | RTFRTF document, opens in a new window (239 Kb)

DROID automatic format identification documentation (including XML schemas) PDFPDF document, opens in a new window (557 Kb) | RTFRTF document, opens in a new window (6 Mb)


Sources for information held on PRONOM are listed for each record. However, The National Archives acknowledges the assistance of the following individuals and organisations in the development of PRONOM and its contents:

Tessella Scientific Software Solutions

Adobe Systems Incorporated (Sascha in Technical Support)
Borland International
Corel Corporation
Crystal Decisions
Jasc Software, Inc.
Microsoft Corporation
National Software Reference Library (US National Institute for Standards and Technology)


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