We Want You Just the Way You Are: The What, Why and When of Fixity


Icons for Archive and Checksum, Designed by Iconathon Los Angeles, California, US 2013. Public Domain

Fixity, the property of a digital file or object being fixed or unchanged, is a cornerstone of digital preservation. Fixity information, from simple file counts or file size values to more precise checksums and cryptographic hashes, is data used to verify whether an object has been altered or degraded.

Many in the preservation community know they should be establishing and checking the fixity of their content, but less understood is how, when and how often? The National Digital Stewardship Alliance Standards and Practices and Infrastructure working groups have published Checking Your Digital Content: What is Fixity and When Should I Be Checking It?  (PDF) to help stewards of digital objects answer these questions in a way that makes sense for their organization based on their needs and resources.

The document includes helpful information on the following topics:

  • Definitions of fixity and fixity information.
  • Eleven reasons to collect, check, maintain and verify fixity information.
  • Seven general approaches to fixity check frequency.
  • Six common fixity information-generating instruments compared against each other.
  • Four places to consider storing and referencing fixity information.

Many thanks to everyone else who participated in the drafting and review of the document:

  • Paula De Stefano, New York University.
  • Carl Fleischhauer, Library of Congress.
  • Andrea Goethals, Harvard University.
  • Michael Kjörling, independent researcher.
  • Nick Krabbenhoeft, Educopia Institute.
  • Chris Lacinak, AVPreserve.
  • Jane Mandelbaum, Library of Congress.
  • Kevin McCarthy, National Archives and Records Administration.
  • Kate Murray, Library of Congress.
  • Vivek Navale, National Archives and Records Administration.
  • Dave Rice, City University of New York.
  • Robin Ruggaber, University of Virginia.
  • Kate Zwaard, Library of Congress.