binary format CDF binary format It is unclear whether, originally, this format was intended to be the ASCII or binary version of the CDF format. As such, this class has been renamed as the binary format, and a new class created (CDF ASCII format) to make both options available. http://www.affymetrix.com/support/developer/powertools/changelog/gcos-agcc/cdf.html, accessed 22 May 2013. The CDF binary format is a binary data format specification created by Affymetrix was created for faster access and smaller file size in comparison to the CDF ASCII format. The values in the file are stored in little-endian format. CDF binary format describes the layout for an Affymetrix GeneChip array. An array may contain Expression, Genotyping, CustomSeq, Copy Number and/or Tag probe sets. All probe set names within an array are unique. Multiple copies of a probe set may exist on a single array as long as each copy has a unique name.