Resources in the Macintosh System Software refers to the data used by applications for there primary usage, such as window structures, menus, constant text strings, code, and much more. The Resource manager manages accessing resources in a very nice way, having resources in the Resource Fork of any file that needs them, and searching for a resource when requested first in the current document, then in the application the document is open in, then in the System file, then in the ROM, this system makes it easy to override resources on a per application, or even per document bases. Along with QuickDraw the Resource Manager is one of the two technologies that really separate the Macintosh System Software from all competition.

The resource fork of a file is a secondary file stream, that is kept separate from the main stream. The Resource Fork has a standard structure that the Resource Manager understands to locate resources, with each resource grouped by type, then by the individual resource ID (there can be multiple resources of the same type). The resource type is a four byte type identifier (usually rendered as four characters)

Some of the most commonly used resource types include:

• CODE: The executable code segments for 680x0 programs.
• APPL: Application Information.
• FREF: Specify a filetype handled by the application.
• BNDL: Specifies bindings within for applications, like the Icon to use and other misc.
• MBAR: Defines a Menu Bar used by the application (may be more than one).
• MENU: Defines the Menu Items in the Menus.
• MDEF: More detailed Menu Definition (not needed in most programs).
• WIND: Define the type, shape and base coords of a Window.
• WDEF: Advanced detailed definition of a Window, allows for much extra definition.
• PICT: Contains a Picture display image (not a raster image).
• ICON: Defines 32x32 pixel Icon mask and image.
• cicn: Defines a color Icon.
• DLOG: Defines a Dialog Box Window.
• ALRT: Defines an Alert Box Window.
• CNTL: Defines a control item.
• CURS: Specify the Monochrome image of a Mouse Cursor and its mask.
• clut: Color Look Up Table.
• snd : Sound sample.
• TEXT: Contains text.
• STR : Contains a string.
• STR#: Contains a list of multiple strings.
• PREF: For storing application Preferences.
• vers: Contains the version number and related information.