PackIt

PackIt is a software data compression utility for archiving and compressing files on the Apple Macintosh platform. It was the first such program to see widespread use on the Mac, and most Mac software archives accepted uploads only in PackIt format for some time. StuffIt, introduced in the summer of 1987, offered much improved compression, and PackIt quickly disappeared.

PackIt was written by Harry Chesley to support an online magazine he was writing for at the time, MacDeveloper. To distribute code and sample applications, he needed to archive a number of files into one for transmission. In the original version this was done in a simple manner, simply placing the Finder file information, data fork and resource fork, if present, in a single stream and placing the resulting "block" in the archive. No compression was used, the program was purely an archiver, similar to the Unix tar utility in concept. Like tar, the format did not include an archive header of any sort. To extract the nth file, PackIt had to read past all of the n-1 files first.