A file with .sitx extension is a compressed archive file created with StuffIt software. This format was introduced as an extension to the original standard Stuffit (.sit) file format and offers comparatively more compression to its predecessor. SITX files are more compact and occupy less space along with the support for 512-bit compression aimed for security. SITX files are recognized by their Internet media types as application/x-stuffitx and application/x-sitx with Uniform Type Identifier as com.stuffit.archive.sitx.
SITX File Format - More Information
STIX are saved in binary file format and were evolved after the usage of the SIT file format. It was introduced by the Aladdin Systems in September 2002 for StuffIt Deluxe 7.0 for Macintosh. This new file format was designed keeping in mind the following objectives:
Support for more compression methods
Support for long file names
Support Unix and Windows file attributes
The updated StuffIt X improved the original StuffIt format by incorporating multiple compression algorithms such as PPM, and BWT to LZW-type compression. The new file format was also equipped with a “block mode” option for protecting against data loss by error correcting “redundancy” options.