a DEFLATE body of compressed data, and an eight-byte 20 See for instance: www.compuphase.com/mp3/sta013.htm#MP3FRAMEHDR. 21 See, for instance: http://en.wikipedia.org/wiki/List_of_archive_formats for a full list, see: http://en. wikipedia.org/wiki/List_of_file_archivers. 22 See, for instance: http://en.wikipedia.org/wiki/ZIP_%28file_format%29. 23 See, for instance: http://en.wikipedia.org/wiki/ZIP_file_format. 24 See, for instance: http://en.wikipedia.org/wiki/Gzip. Overview of data compression standards CRC trailer for error correction. The archive freeware IZArc supports an impressive list of archive file formats, including applications for CD and DVD images. It also pro- vides 256-bit AES encryption, repairing corrupted archives, and several other advanced features. 25 Understandably, the achievable compression rate of any file-archiving programs is strongly dependent on the datafile type (e.g., text, slides, tabulated data, HTML web page, executables, etc.) and anything of a different format that the file might also contain (e.g., raw or uncompressed pictures, equation fields, and other types of embedded additions). An approximate comparison is shown in. 26 This study indicates that pure text files can be zipped down to 19-27% of their original sizes (compression rates of 73-81%), the leaders seemingly being 7-ZIP and RAR, with 19-20% rates. For executables, 7-ZIP champions with 27% squeezing (the other competitors confined to 36-40% ratios), and for raw images this performance is reduced to 50-60%. These figures must, however, be weighted against the coding and decoding times, obviously coming with a higher tax for the champions, but not systematically. Thus, each case is a tricky matter of finding the right trade-off between minimal archival size, the time required to squeeze the file, and the time taken to recover the data as uncompressed. Ideally, compression should be performed as a systematic background routine, in such a way as not to slow down other computer tasks. The external and permanent storage o