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Batch identify file formats with DROID

18 November 2016, Mike Williams

National ArchivesDROID (Digital Record and Object Identification) is an open-source Java-based tool for the batch identification of file formats.

Point the program at a folder tree, it’ll scan the contents and any subfolders and display a detailed report of the contents.

Sounds familiar enough, but this isn’t just another “which folder is hogging all my drive space” tool– it’s a little more interesting than that.

DROID doesn’t come from some unknown developer, for instance– it’s produced by a department of the UK National Archives and has some serious, heavyweight aims. The official site explains:


Files whose internal format doesn’t match their extension are highlighted in the report

DROID is designed to meet the fundamental requirement of any digital repository to be able to identify the precise format of all stored digital objects, and to link that identification to a central registry of technical information about that format and its dependencies.

The key word is “precise”. Other drive visualisers just look at signatures and assume that a PDF is, well, a PDF. DROID will inspect the contents, give you the PDF version number if the extension is correct, and tell you the real format if it isn’t.

This file format ID technology is based on PRONOM, a large, detailed and regularly-updated registry of file format information. (A quick glance at the PRONOM release notes page shows just how detailed this can be.)

This extra information could be very valuable to some, but it comes at a price: speed. Every file must be opened and checked individually, including (by default) the contents of archives, and that makes for a very long scan time.

DROID’s reporting features are also a little disappointing. There are none of the colourful graphs you’d get with the typical consumer drive visualiser: instead you must construct files (“show me MP4 files greater than 25MB modified in the last year”, say) or run the report generator, then wait a very long time for the static text-based results.

If you can use the precise file format identification, this might not matter much. Grab a copy of DROID and try it out– there’s no installation, you can unzip and run it right away.

But if you’re happy to trust your file extensions, you’re not really bothered about format versions, or maybe you just want to view the largest files on your PC, a regular drive visualiser like SpaceSniffer could be a smarter choice.

DROID is an open-source Java-based tool for Windows, Linux and Mac.

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