System suitcase

The System suitcase was one of two principal files comprising the classic Mac OS from the original release to System 9.2.2, the other being the Macintosh Finder. The suitcase was located in the System Folder along with the Finder file and contained keyboard layouts, FKEY resources, sounds, and in System 6, bitmap fonts and Desk Accessories.

Prior to System 7, the Font/DA Mover had to be used to move these into or out of the System suitcase. From System 7 and on, the Finder could open and modify the contents of the file. Over the course of subsequent releases, many of the user-serviceable items stored in the System suitcase were moved into separate folders; this was done by creating individual file types that could contain these resources. System 7.0 allowed sounds, fonts and desk accessories to be moved into their own files; opening a sound file would cause the Finder to play the sound, opening a font would show a preview of the font being used, and the operating system treated Desk Accessories as if they were applications. All Desk Accessories were moved to the new Apple Menu Items folder, along with the Control Panels folder. System 7.1 introduced the Fonts folder, which worked by loading all resources (including fonts) contained in font files or font suitcases found within the Fonts folder as if they were part of the System suitcase.

In System 6, the string "Help! Help! We're being held prisoner in a system software factory!" appears in the data fork of the System file; in System 7, it was updated to "Help! Help! We're still being held prisoner in a system software factory!". Later versions of System 7 alter the message further. A list of credits also follows in each case.

...
Wikipedia