.SIDX File Extension
File TypeStuffIt Archive Index File
What is a SIDX file?
Index file created by StuffIt Deluxe, a file compression and decompression utility; contains a list of reference information about files in a separate file archive; enables users to browse the contents of a particular archive without having to process or decompress it first.
NOTE: SIDX files do not store the files they reference. They only store information about the file contents in a separate archive.