macemu

Open a StuffIt .sit file, without installing StuffIt

A .sit file is a StuffIt archive, and it is the reason most Macintosh software from 1988 to about 2005 is unopenable on a modern computer. Drop one here and it expands on an emulated Macintosh using the real StuffIt Expander — which means the resource forks, the type and creator codes and the folder structure all come out intact, which a modern extractor will usually not manage.

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What StuffIt was, and why it won

Raymond Lau wrote StuffIt in 1987, as a teenager, and it became the compression format of the Macintosh in the way ZIP became the format of the PC. If you downloaded Mac software in the 1990s, you downloaded a .sit. Bulletin boards, AOL, Info-Mac, the University of Michigan mirror — all StuffIt.

It won because it handled the Macintosh file system properly. A ZIP of a Mac application in 1992 was a broken Mac application: the resource fork did not survive the trip. StuffIt archived both forks, the Finder metadata and the folder hierarchy, and it did it well enough that Aladdin Systems built a business on the free Expander and the paid Deluxe.

The format was also revised repeatedly. StuffIt 1.x, 3.x, 5.x and the later StuffIt X (.sitx) are meaningfully different formats sharing a name, which is why a modern tool that claims to open .sit files will often open some of yours and not others.

Why modern tools struggle

There is no official StuffIt implementation left. Aladdin became Allume, Allume was bought by Smith Micro, and the desktop Expander was quietly discontinued. What remains are reverse-engineered readers — the best of them is The Unarchiver's XADMaster engine, which is genuinely good and handles most StuffIt 5 archives.

Two things still go wrong with a modern extractor. The first is coverage: the older StuffIt 1.x compression methods and some StuffIt X variants are patchy. The second, and more common, is that even a successful extraction on Windows or Linux gives you a file with no resource fork, because the host filesystem has nowhere to put one. The application comes out and does not run.

Handing the archive to an actual Macintosh sidesteps both problems. StuffIt Expander on System 7 reads every StuffIt version that existed up to its own, and it puts the forks where they belong because it is writing to an HFS volume that has them.

What happens when you drop a file in

The file is copied into a shared folder on the emulated Macintosh's desktop. StuffIt Expander is already on the boot disk. Double-click the archive and it expands beside itself, exactly as it did in 1995.

If what comes out is an application, double-click it and it runs. If it is a document, the Mac will open it in whatever application on the disk claims its creator code, or tell you it cannot find one.

Nothing is uploaded. The whole thing happens in your browser.

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