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Decompression Help
Tech Library Article #0008 + Created: 29 October 2002 + Modified: 25 January 2006

I downloaded a ".sit" (or ".zip") file from your website, but it won't open! Can you help me?

Before Mac OS X 10.4 (Tiger), most Macs had StuffIt Expander by Allume (formerly Aladdin) Systems pre-installed. StuffIt Expander is the software which opens .sit archive files. Find StuffIt Expander on your hard drive, or if you don't have it, get the latest version for free from If your web browser doesn't automatically expand the .sit file you've downloaded, drag the file onto the StuffIt Expander icon, and it will decompress the file. After the .sit file is decompressed, you will find a folder with the name of the software (e.g. Periodic Table, ConverTable Units, etc.) which contains the decompressed and ready-to-use software!

Also, much of our Mac OS X software is now available in .zip archives. These .zip archives can be opened by double-clicking them if you have Mac OS X 10.3 or later. Unfortunately, the .zip files tend to be slightly larger than the .sit archives.

When we offer the same software as both .zip and .sit archives, the two choices contain the same software, but the .zip files are marked for Mac OS X 10.3 or later because Mac OS X 10.3 or later is needed to open them. Similarly, the .sit files are marked for Mac OS X 10.2.8 or earlier, because later versions of the Mac OS do not have StuffIt Expander pre-installed.

Why don't we use .dmg archives? Well, .dmg archives, or "Disk Images" tend to be larger than even the .zip files for the same data. Additionally, they too have OS compatibility discontinuities--early versions of Mac OS X can't open all .dmg files.

Happily, Mac OS 9 and Mac OS 8 both included StuffIt Expander, so all our Classic Mac software is in one format--.sit. Similarly, Windows XP supports .zip archives natively, so our Windows XP software is all in .zip archives.

ConverTable Units doesn't see plug-in files!

One caveat: StuffIt Expander 7.0 had a bug which caused ConverTable Units plug-in files to become corrupted. This was corrected in StuffIt Expander 7.0.1. ConverTable Units plug-in files expand correctly with StuffIt Expander versions except for 7.0.